theming

Expo Unified Theming

Set up one color system that works on iOS and Android at once. Instead of sprinkling Color.ios.* and Color.android.dynamic.* (or hardcoded hex) all over the app, the user gets semantic tokens (background, text, link, ...) that resolve to the right native color per platform, flip with dark/light automatically, and are read through a single useColors() hook.

This is the pattern from the Platano template, packaged so it drops into any Expo Router app.

What gets installed

Three files (bundled in assets/, adapt them to the project):

• config.ts — the single source of truth. Semantic system tokens set to "native" or a hex, plus brand colors. This is the only file the user edits day to day.
• colors.ts — resolves tokens to real colors per platform, exposes getSystemColor, useSystemColors, the brand helpers, and getNavigationTheme.
• ThemeContext.tsx — ColorsProvider + the useColors() / useTheme() / useBrand() hooks built on React's use.

Plus a small edit to the root _layout.tsx to wire the providers.

The two ideas that make this work

Explain these to the user, because they are the whole point and the two things people get wrong:

1. Re-render on theme change. Native and Material You colors are platform color objects, not strings React can diff. The signal that the theme changed is useColorScheme(). So the resolvers take the color scheme as an argument even when they do not read it: that makes dark/light an explicit dependency, and the value recomputes when the user toggles. The ColorsProvider reads useColorScheme() once near the root, so a toggle re-renders every consumer.

2. Two ThemeProviders, different jobs. ColorsProvider (this skill) feeds useColors() to your components. The navigation ThemeProvider themes the navigation chrome (headers, tab bars, default background). Both live at the root. Wire navigation's with getNavigationTheme(dark) so the chrome matches your tokens. Do not confuse them or drop one. On Expo SDK 56+ the navigation theme bits (ThemeProvider, DarkTheme, DefaultTheme, Theme) import from expo-router/react-navigation; on older SDKs they come from @react-navigation/native instead (see Step 1).

Step 1: Confirm the project, SDK, and the native Color API

This skill targets Expo Router apps on Expo SDK 56 or newer. SDK 56 is where the Color API (iOS system colors + Android Material You) and the expo-router/react-navigation re-exports the templates use both ship. Check the SDK and the Color API before relying on "native" tokens.

# Find the project's app dir and root layout (root-level or under src/)
ls app/_layout.tsx src/app/_layout.tsx 2>/dev/null
 
# Check the installed Expo SDK major version
node -e "console.log('expo', require('expo/package.json').version)"

Branch on what you find:

• SDK 56+ (target): use the templates as written. Navigation theme bits import from expo-router/react-navigation.
• Older than SDK 56: two adjustments are needed.
  1. Import ThemeProvider, DarkTheme, DefaultTheme, and type Theme from @react-navigation/native instead of expo-router/react-navigation — in both colors.ts and _layout.tsx. (Older Expo Router did not re-export them, so you go to React Navigation directly.)
  2. The Color API likely is not present. Either recommend upgrading to SDK 56, or use the hex fallback: keep the files but set the system tokens in config.ts to hex values instead of "native" (no Material You, but everything else works). getBrandColors still works; isAndroidDynamic resolves to false without Color.

Also detect the project's import alias from tsconfig.json (commonly @/* → src/* or the project root). Match that alias when you write imports. If there is no alias, use relative paths.

Step 2: Decide where the files live

Put the three files together in one folder so their relative imports (./config, ./colors) just work. Mirror the project's layout:

• App under src/app/ → create src/theme/.
• App at the root app/ → create theme/ at the root.

Check for an existing theme/colors module or a ThemeProvider first. If the app already has theming, do not clobber it. Read what is there, explain the overlap to the user, and either merge into their setup or place these files under a clearly named folder and let them migrate. Never blindly overwrite.

Step 3: Create the files

Copy the three bundled templates into the chosen folder, adapting:

• import aliases / relative paths to match the project,
• the system tokens and brand colors in config.ts to the user's brand (ask for their brand primary/accent, or keep the sensible defaults and tell them where to change them).

Read each asset and write it into the project (do not just symlink — these are the user's files now):

• assets/config.ts → <theme>/config.ts
• assets/colors.ts → <theme>/colors.ts
• assets/ThemeContext.tsx → <theme>/ThemeContext.tsx

Keep the comments. They explain the re-render trick and the brand/dynamic behavior, which is exactly what a learner needs in their own codebase.

Step 4: Wire the root layout

Edit the existing _layout.tsx surgically — keep every provider, screen, and option already there. The target shape wraps the tree in ColorsProvider and themes navigation from an inner component that reads the color scheme:

Integration rules:

• ColorsProvider must sit above anything that calls useColors(). Putting it at or near the top of RootLayout is safest.
• If the file is already split into RootLayout + an inner component, add the ThemeProvider and useColorScheme() there instead of creating a new inner component.
• If expo-status-bar is not installed and the project does not already manage the status bar, you can skip the StatusBar line.

Step 5: Verify

• Typecheck if available: npx tsc --noEmit (expect no new errors from the three files; the most common issue is a wrong import alias).
• Tell the user to run the app, then toggle the OS appearance (or the simulator dark/light) and confirm colors and the navigation chrome update live. On a physical Android device, changing the wallpaper should shift the Material You palette.

Step 6: Show how to use it

Give the user a short usage snippet (and offer to drop a themed example into one screen if they want to see it immediately):

Outside React (a toast, a one-off style), use the non-hook accessor:

Customizing

• Change a color everywhere: edit config.ts. Set a token to a hex to pin it, or back to "native" to follow the OS.
• Turn off Material You for brand on Android: set brand.useAndroidDynamic: false and the hex brand applies on all platforms.
• Add a token: add it to system in config.ts, then add its iOS / Android / default entries in getNativeDefault and a line in resolveSystemColors inside colors.ts. TypeScript will point out anything you miss.

Notes

• This installs colors and brand only. It deliberately does not add spacing or radius presets or persistence; keep it focused unless the user asks.
• The files become the user's code. Encourage them to read the comments and tweak rather than treat it as a black box. That is the teaching goal of the lesson this skill ships with.