The yellower the better! I want to experiment with a couple of different variables and see which ways are the best. The keyboard doesn't have to be so yellow it is brown, but the more yellow it is the easier it is to that "method X "whitened the keycap L%, "method Y" whitened the keycap M%, and "method Z" whitened N% so method ___ is the best. (That should work as long as the items were equivalent to start with, which is why keycaps are useful for this--you have a bunch of separable objects you can use for experimentation that started out in about the same condition.)