there's a trick to paint something white don't paint something white :-p
start with maybe a neutral or cool grey, then lighten it with careful passes, using very pale cool/blue hues, while keeping some of the shades from grey. then highlight with white, only where it should be the brightest.
To tell the truth I really liked the colour scheme, I like how you used the metallic color (it is metallic color isn't it?) in the armor. The eyes also look great. The only thing you should work a little is the golden color of the weapons and the white of the purity seals. However it looks great, you should make a whole squad!