I kinda wish they were white... the main reason being that now the ROTJ Imperials on Endor seem like they should have been in camo.
Actually, the lack of camo deco on the Biker Scouts CAN be explained (albeit with a pretty thin explanation)....
During the time of the Clone Wars, the Republic is fighting for its existence they will be employing any tactic necessary to give their troops the edge in combat and if giving camo-deco to troopers helps them sneak up on droids in dense forest worlds, then give them camoflaged armor.
However, by the time the OT comes around, the Republic has turned into the Empire and the Empire has been going strong for close to twenty years. There's no need to have your troops worry about fighting another army on the scale of the CIS -- your ONLY problem are those pesky rebels, a movement which you are sure will eventually be squashed and "Fear will keep the systems in line".
At least that's how I rationalize the difference. The Grand Army of the Republic = fighting for their lives and Soliders of the Empire = strike fear into the hearts of the masses and NO ONE will challenge you.