A fairly known Game Boy Color one.

[retrolinkx]

Did you know that if you press a variation of the D-Pad, and the A/B buttons on the start up screen of a Gameboy Color, you can change the pallet that it uses for the games, it has a total of 12 different colour combinations, including Negative, Dark Blue, Pink and Green.

I believe that Game Boy games had the intention of being in colour to a degree but since the Game Boy was grey it wasn't fully utilized, even though it is possible with the Game Boy Color.

Although I cannot show any sort of video evidence, I can give a source.

http://en.wikipedia.org/wiki/Game_Boy_Co..._Boy_games[/code]

I believe this also works on the Game Boy Advance, but I am not sure.