A daily light puzzle
Bend light with mirrors so every target receives exactly the colours it asks for.
Light adds up where it lands. All three together make white.
One new puzzle every day, the same board for everyone, so a result is worth comparing.
No ads. No accounts. No tracking. Nothing leaves your phone.
One puzzle a day, the same one worldwide, so a result is worth comparing. Solve it cleanly enough for long enough and you build two streaks: one for showing up, and one for never slipping.
The board has no text on it at all. Nothing needs translating to be understood, which means the puzzle plays the same in any language.