Revolut • Maxim Kostenko • Jul 19, 2023

Customising Android App UI with Themes

Article Summary

Maxim Kostenko from Revolut reveals how they built one of the most customizable Android apps on the market. Their approach goes far beyond basic dark mode—and it required reverse-engineering Android's own framework.

Most Android apps stop at light/dark themes, but Revolut offers users complete control: system-wide dynamic colors, custom color palettes, and real-time theme switching. This deep dive explains the technical implementation behind each personalization layer, including the challenges of runtime theme changes without official Android APIs.

Key Takeaways

Dynamic colors work via theme overlays, not full Material3 migration
Runtime theme switching requires recreating all activities manually
Custom ColorThemesController mimics private AppCompatDelegate behavior
Theme overlays apply like HashMap keys, replacing specific color tokens
Cross-platform custom themes solve iOS/Android personalization parity

Critical Insight

Revolut achieved maximum Android UI personalization by combining dynamic colors, custom theme overlays, and a custom controller that forces activity recreation—techniques that work without migrating to Material3.

The article includes a complete working demo app on GitHub that implements all three theming approaches, plus the exact code for the ColorThemesController that makes runtime switching possible.

About This Article

Problem

Maxim Kostenko's team at Revolut needed to switch themes at runtime across all active activities. Android's private AppCompatDelegate API only handles light and dark mode, so they needed a different approach.

Solution

They created ColorThemesController using ActivityLifecycleCallbacks to keep track of activity references in a static set. The controller loops through each activity and calls applyDayNight to force them to recreate, which is how Android handles dynamic color and custom theme overlays internally.

Impact

Users can now switch between default, dynamic, and custom Orange themes instantly at runtime. Material Design naming conventions for color tokens like colorPrimary and colorSecondary stay consistent across all screens.