The online game Color Box by eyehook takes the familiar puzzle formula and tosses in a little color theory to brighten things up. Slide and drop squares of color to pile them on the bottom of the screen. Your goal is to make them vanish, but your methods will be a little different. Instead of matching like-colors you must use color theory to change the blocks to white. Fortunately you don't need an art degree to pull this one off.
To get an idea about how things work in Color Box, take a look at the screenshot. If we drop the blue square straight down it will mix with the green and yellow squares on either side, turning them cyan and white respectively. White spaces vanish, letting the blocks on top fall and combine with new squares. It's possible to set up huge chain reactions if you play with this in mind.
When you first start playing Color Box you will do a lot of glancing from the playing field to the color reference chart at the bottom. Fortunately the game isn't timed and puts absolutely no pressure on you to make your next move. You can play with several different color pallets or throw the whole mix in there for an intense challenge.
While it isn't designed to directly teach you color theory, you'll walk away with a little knowledge of how it works. It may be about as useful as calculus to a pop music singer, but artists and web designers will certainly appreciate the help.