1) great colour scheme, very striking. No complaints whatsoever
2) to do black hair, paint it black and do a very small 'line' of white around the crown of the head, especially following the part of the hair, to show light reflection. Don't use colour if you don't have to and above all keep the highlight very thin and small.
2) Studs, grenades, small details, need to be a different colour from the main scheme. I would say go with a metallic brown like tin bitz and bronze/brass for the grenades and a similar colour for the studs and piping on the suit. Basically the only thing lacking on this model is the '3 point colour'. This is a colour that is NOT one of the main colours and is generally found on smaller details in 3 separate spots on the model in order to draw the eye around the model.
4) thin your paints just a hair more. It may just be the picture but the paint looks a bit grainy. Even if it means a couple more layers are needed, it will improve the model immensely.
Don't get the idea that I don't think this is a well done model though Hes. Couldn't be farther from the truth as I really like what you have going so far. This is the forum for constructive criticism though