MasterBoy is a Game Boy emulator for PSP. It allows you to fully recolor your games, not only by selecting one palette for the whole screen, but by recoloring each object on the screen! MasterBoy also emulates the Game Boy Color, Master System and Game Gear. The SMS/GG emulation is based on MMSPlus, and has been improved a lot since then.

http://www.neoflash.com/forum/index.php/topic,4588.0.html