Carp can be very difficult to catch on the fly. I think this is why they have been nicknamed " freshwater bonefish " because of the stealth you need to stalk them, cast ahead of them and then the patience to wait until they just pick up your fly. Of course there is times when they wont be hard at all but i doubt this is a regular occurance.
I would use something in Black, Green (darker), Maroon or a Darker Brown and weight it so you can get it on the bottom in front of FEEDING fish not the ones just swimming around. The trick is the strip set for setting the hook as oppose to just lifting the rod like we all do for trout, salmon, steelhead.
I have done a bunch of reading lately on catching carp on the fly because i plan on hunting some down this year