I would say hair color would have to depend on what sort of style/feel you're going for and which version of Cleo it is.
For the dolly hair hanks, for most styles two RD hanks is sufficient. If you are going super long you might need three. It's possible you could get away with one on a very short style, but I find it's better to have extra then not enough, plus it's often a bit easier to use slightly longer plugs and cut the hair afterwards then too short and have hair constantly falling out of your grip.