dark blue wash jeans is definitely my preference. Guys look amazing in them (assuming they're not falling off his body) - it says kinda casual, but you care enough to clean up and you care about how you come across to others. Black slacks would work well too if you're going really fancy, but if you're going out on a date or something similar, go for the dark jeans :)
Black slacks. If you are going for dressy that is. If you want to make it more casual, wear it half unbuttoned with a white shirt underneath and jeans. For some reason in my head, the outfit is set off by a sharks tooth necklace... Idk. Anyway. I'm assuming you are going for dressy though. Avoid brown and NEVER wear gray with gray. If it is the wrong shade (likely) you will clash, and if you have the same shade, you'll look like you're wearing pajamas or a jumpsuit... lol
tan/khaki color jeans or like black jeans (I only say jeans because I don't know how dressed up you wanna be) slacks are always good too. if you wear sneakers like vans or converse just make sure they are not too dirty or old looking. if its super nice wear like a cool black tie. I think that would look good, the grey shirt, black jeans, either nice shoes or black vans/converse a black tie. ( you could even have the shirt kinda tucked in...hope I helped!