Ok, time to be a Star Wars geek. Expanded universe and Revenge of the Sith novel wise, Mace explains that Vaapad, the seventh lightsaber form that he invented/modified, uses his anger and love of battle to fuel and focus himself in combat. So you can have a arguement for Red. But he's still able to control himself and stay on the light path, so Green works well too.
Vader as Yellow works well, since he caused so much fear throughout the entire galaxy while working as the Emperor's right hand man. Sure, back when he was Anakin Red would have worked, but Vader during the movies? Coldly disspassionate.