Blendoku is a mobile puzzle game that is free for Android and iOS.
The object is to organize colors by saturation, shade and hue. While it sounds simple, things get tricky pretty quick; and next thing you know you're immersed in a Sudoku-crossword rainbow puzzle. Not sure you're grasping the concept? Check out this brief demo video.
If you've got some free time (or perhaps a lot of free time), give it a go and let me know what you think. Already feel like you're becoming a color master? Or was this just a (visually stimulating) waste of time?
Note: This game isn't color blind friendly (yet), but according to this Mashable article, creators Rod Green and Yeong-Hao Han say they're working on a way to shift the colors so that everyone can play.