A Guro Lolita outfit can really be pulled-off in any colour, but white really does look fantastic if you want to have some blood splatters! (If you're worried about getting blood splatters on your lovely dress, perhaps you could make yourself a small apron to splatter.)
Although Guro Lolita may sound costume-y, just like other Lolita styles it is a part of a fashion, and not a costume, and follows all of the guidelines that the other styles do.This style really is not acceptable for a lot of group Lolita activities such as tea-parties, and special events.
Make-up for this style is really up to you, as long as you're still fairly modest the sky is the limit. Fake blood is a great item to have for this style, and can be purchased at most local party stores.