I think their might be variants pigment-wise of the Engineers, as the Engineer seen at the beginning seemed very white, while the one we see more of at the end looked like his skin was so light blue it was almost white, but not quite. At least that's how it looked to me.
As for the Deacon, it was in its chestbuster stage when we saw it, so it may have taken on host pigmentation at this early stage before molting occurred and it matured. Since all the human spawned chestbusters start out with a light tan color in the films, could it be possible they would start out with host pigment since I don't think we've seen a chestbuster from a non-white individual before it had already matured into an adult Xenomorph in the movies(correct me if I'm wrong).
I think part of the reason I really want/wish/hope they are actually blue is because I am so tired of aliens just being white people with only minor differences physically(which isn't that much of a difference still). It is just so unimaginative it kills me on the inside.