Fix color scheme default (#4185)

Small follower for #4184

### Change type

- [x] `bugfix`

packages/tldraw/src/lib/ui/components/ColorSchemeMenu.tsx

@@ -16,7 +16,10 @@ export function ColorSchemeMenu() {
 	const trackEvent = useUiEvents()
 	const currentColorScheme = useValue(
 		'colorScheme',
-		() => editor.user.getUserPreferences().colorScheme ?? 'system',
+		() =>
+			editor.user.getUserPreferences().colorScheme ?? editor.user.getIsDarkMode()
+				? 'dark'
+				: 'light',
 		[editor]
 	)