Mattermost UI: Customization Guide for Teams

Mattermost has a flexible, three-pane interface you can customize to match your team's workflow. The platform offers five built-in themes and granular control over colors, fonts, and layouts. You don't need to code to make it yours.

What Is the Mattermost User Interface?

Mattermost's user interface is built around a three-pane layout that organizes channels, conversations, and files in a single workspace. The left sidebar contains your channels and direct messages. The center pane displays message threads and content. The right sidebar shows search results, pinned posts, or expanded threads. This layout is familiar if you've used Slack, but Mattermost gives you deeper control over how it looks and behaves.

The interface prioritizes speed and clarity. You see all your teams and channels on the left, switch between them instantly, and read threaded conversations without leaving the page. Mobile and desktop apps render the same layout but adapt to screen size. On a phone, the sidebar collapses into a menu icon. On a desktop, all three panes are visible at once.

Mattermost is open-source, deployed on 39,000+ GitHub stars and active in 23,229 commits. That maturity means the UI is stable and well-tested. Teams like Uber (handling 70,000 concurrent users), Samsung, GitLab, and the US Department of Defense rely on it daily. The interface handles high-volume communication without lag.

You're not locked into a default look. Mattermost assumes you'll customize the theme to reflect your company's colors, identity, or workflow preferences. Out of the box, five built-in themes are available. Beyond that, you can build a custom theme by editing CSS values directly in the Settings panel.

Mattermost UI Layout Elements Explained

The left sidebar shows your team name at the top, followed by channels, direct messages, and saved posts. You can collapse it to gain center-pane width. Channels are sorted by recency unless you pin important ones to the top. Clicking a channel opens it in the center pane.

The center channel pane displays messages in chronological order. You can scroll back weeks or months using the search bar. Each message shows the sender's name, avatar, timestamp, and reactions. Threaded replies don't clutter the main feed, keeping conversations organized. The message input box sits at the bottom with options to attach files, add emojis, or format text (bold, italic, code blocks).

The right sidebar varies depending on what you're doing. By default, it shows pinned posts for the current channel. Click on a message to open a thread in the right pane, keeping the main channel visible. Search results appear here too. In settings, you can pin it closed or let it auto-hide to maximize the center pane on smaller screens.

Mobile apps render a single-pane interface. You see the sidebar, tap a channel, and the center pane fills the screen. Tap the back arrow to return to the channel list. The right sidebar collapses into an action menu accessible via a three-dot icon. Desktop apps (Windows, macOS, Linux) show all three panes by default and include features like desktop notifications, browser-style tabs, and offline message queueing that the web client lacks.

The top navigation bar displays the current channel name, search, and a menu icon. Clicking the menu opens options for channel settings, members, pinned posts, and file search. Right-clicking a channel name offers quick actions like muting, favoriting, or leaving.

These elements are static in layout but fully customizable in color and typography. You can change the sidebar background, text color, active channel highlight, center pane background, link color, and code-block theme. Every color can be set to any hex value, giving you pixel-perfect branding control.

Built-in Themes: What's Included Out of the Box

Mattermost ships with five preloaded themes: Denim, Sapphire, Quartz, Indigo, and Onyx. Each one is a complete color palette tuned for readability and visual comfort. Denim is the default, a light blue-gray scheme. Sapphire is a darker blue with higher contrast. Quartz is a minimalist grayscale. Indigo is bold purple. Onyx is pure dark gray, nearly black.

To switch themes, go to Settings > Display > Theme and choose one from the dropdown. Your preference syncs across devices if you're logged into the same account. Team admins can set a default theme for all new users, but individuals can always override it.

If none of the built-in themes match your brand, don't switch back to Denim. Instead, customize one by clicking "Edit" next to the theme name. A color picker opens for each UI element: sidebar background, sidebar text, active channel highlight, center channel background, link color, button background, code-block background, and more. You can copy hex color values from your brand guidelines and paste them in. The preview updates in real-time, showing how the new colors look.

Theme customization is a per-user setting by default. Each person can pick their own theme and colors. But admins can lock the theme at the workspace level so everyone sees the same branding. This is useful for enterprise teams where consistency matters for training or compliance.

Dark mode is available on desktop apps (Windows, macOS, Linux) via a system preference or app setting. The web client inherits your OS dark mode choice if it's enabled, but some browsers don't support it. The mobile apps follow your device's dark mode setting automatically.

Community themes are also available. Users have contributed dozens to GitHub and the Mattermost forums, including themes inspired by Discord, GitHub, Gruvbox, Monokai, and One Dark. Installing a community theme requires copying a JSON blob and pasting it in the theme editor. No command line or file upload needed.

How to Customize Mattermost UI: Step-by-Step Guide

Mattermost customization happens entirely in the Settings panel. No plugins, no code deployment, no server restart. Here's how to build a custom theme.

Step 1: Open Settings Click your avatar in the top-right corner and select "Settings". On mobile, tap the menu icon (three horizontal lines) and scroll to "Settings".

Step 2: Navigate to Display In the Settings menu, select "Display" in the left sidebar. You'll see options for Theme, Font Size, Timezone, and Message Display. Click on "Theme".

Step 3: Choose a Base Theme You can customize any of the five built-in themes or start from scratch. If you're building a dark theme for a night-shift team, start with Onyx or Indigo as the base. If you want something light, start with Quartz or Sapphire. The base theme sets reasonable defaults that you'll tweak.

Step 4: Edit Colors Click the "Edit" button next to your chosen theme. A panel opens with color fields for each UI element. Here are the key ones:

• Sidebar Styles: Background color (typically a dark color like #2f3e50), Text color (#ffffff for contrast), Active border color (often your brand color, like #0066cc).
• Center Channel Styles: Background color (usually #ffffff or #f8f8f8), Text color (#333333), Separator color (#eeeeee for light themes).
• Link and Button Styles: Link color (your brand blue, like #0066cc), Button background (brand color), Button text (usually white, #ffffff).
• Code Theme: Choose from GitHub, Monokai, Solarized-Dark, or Solarized-Light. This sets the syntax highlighting for code blocks in messages.

Step 5: Test in Real Time As you change each color, the preview pane on the right shows how it looks. Check readability: can you read black text on your sidebar background? Is the link color distinct from regular text? Hover over elements in the preview to see them highlighted. Click on a mock message to see how threads appear.

Step 6: Save and Apply Click "Save" at the bottom of the panel. Your theme is now active. It syncs to all your devices if you're logged in.

Step 7: Share with Your Team Your custom theme is personal by default. To share it with your team, click "Edit" again and scroll to the bottom. You'll see a JSON block containing all the color values. Copy this JSON and share it via Slack, email, or documentation. Each team member can paste it into their own theme editor to use the same colors.

Advanced: Locking Themes at the Workspace Level If you're an admin, you can enforce a theme for all users. Go to System Console > Customization > Display and select a default theme. New users will start with this theme, though they can still customize it for themselves. To prevent customization entirely, set "Allow Theme Selection" to false in the same panel.

Common Pitfalls Don't choose colors that are too similar to your text color for the background. Dark gray text on a dark blue sidebar is hard to read. Test your theme on a 15-inch laptop screen, not just your 4K monitor. Mobile rendering may differ. If you mess up, switch back to Denim or another built-in theme and start over. There's no "undo" for theme changes, but you can always reset.

Performance Considerations Mattermost doesn't penalize you for heavy customization. Colors and fonts don't increase server load or client-side rendering time. A custom theme loads as fast as a built-in one. You can change themes dozens of times without degrading performance.

Community Themes & Advanced Customization

The Mattermost community has contributed 10+ pre-built themes available on GitHub and the official forums. Popular ones include Discord Dark, One Dark, Gruvbox (for developers), GitHub Light, and Monokai. These themes are designed by people who wanted specific aesthetics and shared them for others to use.

To install a community theme, find its JSON on GitHub or a forum post. Copy the entire color object (it looks like {"sidebarBg": "#2f3e50",...}). In Mattermost Settings > Display > Theme, click "Edit" on any theme, scroll to the bottom, and paste the JSON into the "Theme Code" field. Click "Save" and the colors apply instantly.

You're not locked into a community theme as-is. Paste it, then tweak the colors for your needs. If Discord Dark is almost perfect but the sidebar is too dark for your office lighting, adjust the hex value and save again.

Beyond themes, you can customize other UI elements via plugins. Plugins can add custom buttons, sidebars, or workflows. For example, a plugin might add a project management widget to the right sidebar or a custom command to post templated messages. Installing a plugin requires admin access and is done via System Console > Plugins > Plugin Marketplace or by uploading a plugin file. Plugins do require more technical knowledge than themes, so they're best handled by your ops team.

You can also customize emojis, slash commands, and integrations. Slash commands are shortcuts you type in the message box, like "/remind me at 3pm" or "/giphy mattermost". Admins can create custom commands that trigger external workflows. Integrations connect Mattermost to tools like Jira, GitHub, GitLab, or your own internal APIs. These are UI extensions, not UI customization in the traditional sense, but they affect how you interact with Mattermost daily.

Mattermost UI vs. Slack, Teams & Discord

If you're comparing Mattermost to Slack, the UI is recognizably similar but Mattermost offers more control. Slack's interface is polished out of the box: clean fonts, good spacing, and a cohesive design language. Mattermost's default UI is functional but plainer. However, Mattermost gives you granular color control that Slack doesn't. Slack allows limited theme customization (a few preset color palettes), while Mattermost lets you set hex colors for every UI element. For teams that want their collaboration tool to feel like part of their brand, Mattermost wins.

Teams (Microsoft) has a complex interface with tabs, nested channels, and multiple sidebar regions. It's more powerful but harder to navigate. Mattermost is simpler: one channel list on the left, one conversation in the center. If your team values simplicity and speed, Mattermost's UI is cleaner than Teams.

Discord's UI is gaming-centric with animated reactions, emojis, and a playful aesthetic. Mattermost's UI is business-focused: no animations, plain emojis, formal color schemes. Discord feels more casual; Mattermost feels more professional. Both offer custom themes, but Discord's theming is limited to the community via CSS mods (not officially supported). Mattermost's theming is built-in and supported by the core team.

All four platforms (Mattermost, Slack, Teams, Discord) use three-pane layouts as the baseline. The differences are in polish, customization depth, and use-case fit. Slack is best if you want it to "just work" without thinking about look and feel. Teams is best if you're already in the Microsoft ecosystem. Discord is best for gaming or casual communities. Mattermost is best if you want a professional, customizable, open-source collaboration tool.

UI Customization Best Practices & Gotchas

Customization is powerful, but too much of it confuses your team. Here are practices that work.

Do: Start with a built-in theme. Don't start from scratch with a blank color palette. Choose Denim or Sapphire and tweak one or two colors. This keeps the UI visually cohesive.

Do: Match your brand, but don't overcomplicate. Use your brand's primary color for the active channel highlight or link color. That's enough. You don't need to make the sidebar your brand color and the center pane a different accent. Simplicity wins.

Do: Test on multiple devices. Export your theme JSON and paste it on a coworker's phone and laptop. Does the sidebar color look good at full brightness? Does it hurt to look at under office lights? Adjust if needed.

Do: Document the theme. Save the theme JSON somewhere (a wiki, a pinned message in #general, a GitHub repo). If a new hire joins, they can apply the team theme in 30 seconds by copy-pasting JSON. This saves onboarding friction.

Don't: Change colors constantly. Every time you change the theme, everyone sees a visual shift. It's jarring. Pick a theme and stick with it. If you do change it, give the team a heads-up.

Don't: Use colors with low contrast. If your sidebar is dark gray (#333333) and your text is medium gray (#666666), your team will struggle to read it. Tools like WebAIM's Contrast Checker can verify that your colors meet WCAG AA standards (4.5:1 contrast ratio for text).

Don't: Customize beyond themes. Plugins can extend the UI further, but each one you install adds complexity. Stick with the core theme customization unless a plugin solves a specific business need.

Troubleshooting: I changed the theme and now I can't read anything. Go to Settings > Display > Theme and switch to Denim (the safe default). Then carefully adjust one color at a time and test readability.

Troubleshooting: My team's custom theme isn't showing on new devices. Themes are per-user, not per-workspace. Each person needs to paste the theme JSON in their own Settings. An admin can set a default workspace theme, but individuals must opt in. To avoid this friction, have your ops team set the default theme in System Console > Customization > Display.

Performance: Will a custom theme slow down Mattermost? No. Colors and fonts are CSS changes only. They don't impact server performance or client-side rendering. Even a complex theme with many custom colors loads in milliseconds.

Running Mattermost UI at Scale: Self-Hosted vs. Managed

When you self-host Mattermost, you own the UI customization. You can theme it however you want, but you also own the backups, updates, and day-to-day operations. If your server goes down, your custom theme goes with it.

Managed Mattermost hosting (like Opsily's offering on /hosting/mattermost) handles infrastructure for you. You still customize the UI fully. Your theme is backed up automatically with your data. When Mattermost releases a new version, we update the server, and your custom theme persists. You're not managing Docker, Kubernetes, SSL certificates, or database backups. Your ops team can focus on features, not infrastructure.

Theme changes are instant in both setups. Whether you're self-hosted or managed, editing a color and clicking Save applies it to your workspace in seconds. The difference is in reliability and support. Self-hosted teams can hit issues like corrupted theme JSON or theme bugs after an upgrade. Managed hosting includes support: if something breaks, the hosting team can recover your theme from backups or help you troubleshoot.

For teams under 100 people, a managed hosting platform eliminates weeks of setup and ongoing maintenance. You get the UI customization you want without the ops burden. For enterprises with dedicated ops teams, self-hosting offers more control and often lower per-user costs at scale.

Frequently Asked Questions

What is the Mattermost user interface?

Mattermost has a three-pane layout: left sidebar for channels and messages, center pane for conversations, right pane for threads and search results. It's customizable via built-in themes and color pickers. No coding required.

How do I customize the Mattermost UI?

Go to Settings > Display > Theme. Choose a built-in theme, click "Edit", and set colors for each UI element (sidebar, center channel, links, buttons). Save and the theme applies instantly. Share the theme JSON with teammates so they can use the same colors.

Does Mattermost have pre-made themes?

Yes. Five built-in themes (Denim, Sapphire, Quartz, Indigo, Onyx) ship with Mattermost. The community has created 10+ additional themes (Discord Dark, One Dark, Gruvbox, GitHub Light) available on GitHub.

Can I change the Mattermost sidebar color?

Yes. In Settings > Display > Theme, click "Edit" and adjust "Sidebar Styles" background color. Any hex value works. You can also change sidebar text color and active channel highlight separately.

How does Mattermost UI compare to Slack?

Slack's UI is more polished out of the box but offers limited customization. Mattermost's default UI is plainer but gives you granular control over colors. Both use three-pane layouts. Mattermost is better if you want to brand the tool to match your company.

Is Mattermost UI available on mobile?

Yes. Mobile apps (iOS, Android) render a single-pane interface that adapts to screen size. The sidebar collapses into a menu. All your custom colors sync to mobile. Some features (desktop notifications, offline message queueing) are desktop-only.

How do I share a custom Mattermost theme with my team?

Click Settings > Display > Theme, click "Edit", and scroll to the bottom to see the theme JSON. Copy it and share it via email, a pinned message, or a wiki. Teammates can paste it into their own theme editor to apply the same colors.

Will customizing the Mattermost UI impact performance?

No. Theme customization is CSS-only and has no impact on server load or rendering speed. You can customize freely without worrying about performance.

The Bottom Line

Mattermost's UI is straightforward to customize and gives you control that Slack doesn't. You can build a cohesive, branded workspace in minutes by adjusting colors and fonts. For teams that care about look and feel, that depth of customization is a major win.

Start with a built-in theme, tweak one or two colors to match your brand, and document the theme JSON so new hires can use it. Don't overcomplicate it: simplicity makes the UI faster to learn and use. Test your custom theme on desktop and mobile before rolling it out team-wide.

If you're evaluating Mattermost for your organization, UI customization is one of its strengths. You can make it feel like your tool, not someone else's. Ready to deploy Mattermost with full UI customization support? Check out Opsily's managed Mattermost hosting.