a dark colored scratch? what the hell do you have planned for your gba ha ha ha ha, lol.
minor nicks and scratches shouldn't be a big deal on light colors, especially if it is that way throughout the casing and not just paint. if it is paint over a darker color then yes it would show more on the platinum but if the plastic is all that color it shoould still show less. a deeper scratch especially. have you ever taken a knife or sharp object to dark plastic? the edges tend to lighten in color of the scratch making it stand out a little bit more. if it is just a light scratchh or nick, niether color would make much of a diffenece. if you plan to fill your scratches in with dirt or a marker or whatever then yes, on the lighter system you would see it.
i guess my point is just that i would not worry about scratches enough to choose a color over it.