Thanks for the reply!
Just for reference, do you reckon it's just because they look "dirty" that they look grey here? The trousers definitely don't match the lighter parts of his shirt, I'd say they're closer to the darker panels.
I'll try and get some pictures of my progress so far up once I've got access to my kit. I'm not going 100% accurate in terms of tactical gear (as I have a rule about only cosplaying with gear I'm likely to get some use out of afterwards) but I'm hoping to get the clothing down as close as possible!