This button will have more features in the next version. Monochrome games for the original Gameboy had four shades of grey.
But with VBA-Wii you can define your own colour palettes for these games. Games for Gameboy Advance, Gameboy Color, and Super Gameboy, are already in colour, and changing palettes for these games will have no effect.
Unfortunately, some Super Gameboy games are programmed in greyscale and that can’t be changed yet. Looking for a brief and simple tutorial how to emulate Game Boy Advance entertainment on your computer or laptop for free?