Changing your Slack theme takes about ten seconds once you know where the setting lives — and ten minutes of confused clicking if you don't. This is the ten-second version. Here's how to change your Slack theme on desktop and in the browser, what you can and can't change on your phone, how to get the same look across every workspace, how to hand a theme to your team with one click, and what to do when the theme refuses to update.
If you're here for the palettes rather than the mechanics, jump to our gallery of the best Slack themes or the field-by-field breakdown in Slack theme colors. This post is the plumbing.
How to Change Your Slack Theme on Desktop
The desktop app and the browser version share the same settings, so these steps work in both.
- Click your workspace name in the top-left corner and open Preferences (or press
Ctrl+,on Windows and Linux,Cmd+,on Mac). - Open the Themes section — some versions label it Appearance. It's the one with color swatches.
- Pick a mode: Light, Dark, or Sync with system. This controls the message pane, the big area where you read and type.
- Scroll to the bundled sidebar themes and click one, or expand Custom theme to paste your own.
That's it. There's no save button; the change applies the moment you click, no restart needed. If nothing changed, skip ahead to the troubleshooting section.
Using a custom theme string
The Custom theme box takes eight six-digit hex colors, comma-separated, no spaces, no trailing comma. Here's one — the Propsly brand palette, teal sidebar and hot-pink active channel:
#167891,#12657F,#FF5FA2,#FFFFFF,#11515F,#E9F7F6,#8BD6D4,#FF5FA2
Slack reads those eight values strictly in order: column background, hover menu background, active item, active item text, hover item, text color, active presence dot, and mention badge. The first is most of what you see; the third is the highlight bar on the channel you're in; the sixth is every channel name; the eighth is the unread pill that's supposed to interrupt you. Slack previews live as you edit, so change one value at a time and you can tune a theme in a few minutes. The full explanation of each field, plus strings grouped by color family, is in our Slack theme colors guide.
Two things people miss the first time. Custom themes color the sidebar only — the message pane follows the Light/Dark/System choice from step three, so a dark sidebar string with light mode on looks half-finished. And Slack only accepts six-digit hex with a leading #: shorthand like #FFF is ignored, and one bad field can quietly invalidate the whole string.
How to Change Your Slack Theme on iPhone and Android
Honest answer, since a lot of people search "change slack theme on iphone" and end up disappointed: the mobile apps let you change appearance, not theme.
On iOS and Android, open the You tab, go into Preferences, and find the appearance or dark mode option. You can choose light, dark, or follow the phone's system setting. That's the whole menu. Custom sidebar strings don't apply on mobile at all — there's no field to paste into, and your phone's sidebar stays stock no matter how glorious your desktop looks.
So "my phone's Slack should be dark" is covered. "My phone's Slack should be teal and pink" isn't something Slack offers today, and any app claiming otherwise deserves a skeptical look — we cover what third-party skins actually can and can't do in our Slack skins explainer.
Syncing Your Theme Across Devices and Workspaces
This trips up almost everyone. A Slack theme is per workspace, per person. It's not a global setting for "your Slack" — it's a setting for you in this workspace. If you're in four workspaces, each has its own theme, and changing one leaves the other three untouched.
- Same workspace, desktop app and browser: the theme generally follows you, since Slack stores it with your account for that workspace. If it doesn't show up, sign out and back in, or just re-paste.
- Same workspace, a fresh install on a second computer: if the sidebar comes up default, re-paste. Keep your string somewhere findable — a note to yourself in Slack works well.
- Different workspaces: you paste per workspace, every time. There's no "apply to all."
- Mobile: nothing to sync, since custom themes don't run there.
The per-workspace rule is a feature. The best use of Slack themes is giving every workspace a different color so you always know where you are before you type: company workspace in brand colors, client workspaces in theirs, the community server in something loud, the on-call workspace in something alarming. You'll never post a joke into a client's #general again.
How to Share a Slack Theme With Your Team
You don't need to walk anyone through Preferences. Paste a valid theme string into any channel or DM and Slack recognizes the format and attaches a "Switch sidebar theme" button under the message. One click and they're wearing it; click a different string and they're wearing that instead, which doubles as an instant undo.
Admins can't enforce a theme workspace-wide, and you shouldn't want to. What works better is a small ritual:
- Pin the team theme in #general or drop the string in the channel topic. New hires paste it on day one and instantly look like everyone else's Slack.
- Start a #themes channel. People post the strings they're using, argue about them, and steal the good ones. It's the lowest-effort culture channel we've seen, and it sits nicely alongside the other small rituals that give a distributed team a pulse.
Slack Theme Not Working, Won't Update, or Keeps Changing
Most "my Slack theme won't update" problems are one of these seven things. Check them in order; the first three cover the vast majority.
1. The theme string is malformed
The number one cause of a pasted theme doing nothing, or only partly applying. Slack silently ignores anything it can't parse. Check that you have exactly eight values, each is # plus exactly six hex characters, commas sit between values with no spaces, and there's nothing after the eighth — no trailing comma, no period from the end of a sentence. Copying out of a document is where stray characters sneak in.
2. You're in the wrong workspace
Because themes are per workspace, it's easy to paste a string, look at a different workspace's sidebar, and conclude nothing happened. Check which workspace icon is highlighted in the far-left rail first.
3. System appearance sync is overriding your choice
If your theme "keeps changing" on its own — dark in the evening, light in the morning — you almost certainly have Sync with system on, and your operating system switches appearance on a schedule. That's the OS, not Slack. Go back to Preferences, then Themes, and pick Light or Dark explicitly. The same thing happens on phones with automatic dark mode enabled.
4. You changed the mode but not the sidebar (or the reverse)
Light/Dark/System controls the message pane; the custom string controls the sidebar. Switched to Dark and the sidebar didn't budge? Expected — pick a dark sidebar theme too. Pasted a dark string and the message area is still white? Switch the mode. Two separate dials on the same settings page.
5. Browser Slack versus the desktop app
They share the same theme for the same workspace, but browsers add their own layer. An extension that "darkens every website" will happily override Slack's colors and make your theme look muddy or broken. Disable it for Slack's domain and reload. Extensions are the usual culprit when a theme looks right in the app and wrong in Chrome.
6. Slack is out of date
Theme settings have moved and been relabeled over the years, and an old desktop build occasionally fails to apply changes cleanly. Update the app (the browser version is always current), then try again.
7. Stale cache
Last resort. Quit Slack completely — actually quit, not just close the window — and reopen. If that fails, clear the app's cache from its troubleshooting menu (in a browser, hard-refresh with Ctrl+Shift+R / Cmd+Shift+R), sign out, sign back in, and paste once more. We've never seen a valid theme survive that sequence without applying.
What Is the Default Slack Theme?
The current default is Slack's own purple-toned sidebar, paired with whatever Light/Dark/System mode you picked when you first opened the app — many people run "Sync with system" without realizing they chose it. The original muted plum-and-teal "Aubergine" sidebar that shipped for years is no longer the default, but you can reconstruct it from a string; there's one in the theme colors guide. To go back, open Themes and click the default swatch. There's no reset button; picking any bundled theme replaces whatever you had.
A Themed Workspace Is the Cheapest Morale Win
A workspace that looks like yours — brand colors in the sidebar, a #themes channel — is a real, if tiny, quality-of-life improvement for a tool people stare at all day. It costs nothing and takes ten seconds. If you're setting up a new workspace, do it alongside the defaults in our guide to getting started with Slack, tidy the sidebar itself with custom sidebar sections, and skim the Slack tips and tricks that make the daily grind faster.
The second-cheapest morale win is peer recognition, and here's the disclosure: we build Propsly, a Slack recognition bot, so yes, it's ours. Same idea as theming — make the place your team lives all day feel a little better — pointed at people instead of pixels. Anyone types /props @maria +20 for shipping the migration #teamwork, the give lands in a public #wins channel, and everyone gets 200 props a month to hand out, free for unlimited users. A teal-and-pink sidebar looks great. A feed lighting up inside it is the part people remember.
But first: go paste a theme. Preferences, Themes, ten seconds, done.