From what I have heard the south platte carp are pretty finicky. You might try a San Juan worm...I know one of my CO buddies does well on his version (the trouser worm). you can check his pattern out here:

http://www.flycarpin.com/2011/03/mct...carp-worm.html

My go to is a green soft hackle, but the carp I fish for are a little less aggressive than the south platte fish from what I have heard. Good luck man!