Wow. as usual this is a stunning piece of artwork. As it was said earlier the yellow is just right for the Imperial Fists, although I do find it funny that someone who has a Iron Warriors army would paint up a imperial fist model? Maybe it's to be used as target practice....
Personally I would do green eyes, rather dark with a strong sharpe edgeing highlight along the top of the eye piece. Also are you keeping the helmet stripe white? How about the shoulder armour's edges'? Are they going to stay black?
The weathering looks spot on. Thank you for sharing this with us. =o]