Thanks every one, but most importantly thanks for the turquoise suggestion.
The white was purely organic, I liked the idea of porcelain face masks and once i'd painted them they really worked, but the model became unbalanced. Therefore, I ended up balancing the model by painting white shoulder and knee pads with white casing for the weapons.
Diamonds are actually easier to paint than they look, especially after watching Duncan on warhammer TV do them. Although if you've never done any free hand I really wouldn't suggest trying to paint diamonds. My advise would be to get some free hand practice with vehicle squad markings before trying to do diamonds.