Wayne,
Blue: Been there, done that. But it's a nice background colour nonetheless.
Grey: Nice. Not hard on the eyes, and very ... serene.
Yellow: AAARRRGGGHHH!!!! My eyes!!! Must ... avert ... my ... eyes!!! Now I know what it feels like to have a hangover and be looking at a bright computer screen at the same time. :-P
My vote: Go for grey, or stick with the current blue. I prefer grey, but I'd be happy either way.
AmiGod
