Turn
Tap a ring to turn it one pane to the right. Drag a ring to spin it. Keys: 1 to 5 pick a ring, arrows turn it, Z undoes, R resets, N opens the next window.
How light mixes
A colour is made of ruby, emerald and sapphire. Glass keeps only the parts it has. Lights that meet keep every part either had. This is light, not paint.