We're All Plain! 2 SE is a little level-based Flash puzzler created for the Global Game Jam. On each level, there are an array of colored orbs. They're on springs; you can pull one back and let it go. If it intercepts an orb of the complementary color (red/gree, blue/orange, purple/yellow), both turn white. To clear the level, you must turn all orbs white.
In addition, banging an orb into a non-complementary color changes the target into the intermediate color (e.g., banging blue into red turns the red orb purple). At higher levels, the springs have limited pull-back, so quite often you cannot change to white immediately -- instead, you must manipulate the orbs, changing to intermediate colors to establish an array that can then be turned white.
The resulting puzzles are actually quite challenging, given the simplicity of the underlying scheme. Graphic designers, to whom the color wheel is second nature, will doubtless find it easier than I, of course.