Messing with VBAdvance

How do you set it so GBC colors show on a GB game?

While you can't use the GBC palettes directly with old GB games, you canessentially set them up through the Colors menu. Just go to Options > Gameboy > Colors... and you set up two custom palettes, as well as the main palette. Naturally, though, you only get eight colors: four for sprites, and four for the background.

DRAT.

...Although I just realize, you were referring to the pre-GBC games, such as Kirby's Dream Land, Tetris, and Super Mario Land, right? 'Cause VBA should automatically use Super Game Boy and GBC palettes for games that have support for them.

PKMN Blue goes grey

Quite odd. Well, in that case, try changing it from Automatic to SGB or SGB2. That should hopefully force it to load the Super Game Boy palette, instead of forcing the original GB one. Although I don't see why you'd have to; I don't have those kinds of problems with Donkey Kong '94 (also a dual GB/SGB game).