Training is more important than color coding, in my opinion. We spend quite a bit of time learning how to use our new equipment. All three of us are qualified climbers, riggers, and groundies. We take turns on the climbing ropes, rigging, bucking, and loading/hauling. All of my guys know how to run the tractor, dump truck, saws, etc.
We purchased a set of color coded DMM Ultra-O biners from TreeStuff for use during training. It's somewhat helpful, as the instructor doesn't have to stand in the way, or block the view of the others. Knot tying and knot selection is something we spend a lot of time with, but we also train on the climbing gear. Color coded biners help a lot when the climber is just out of reach of the instructor.
All of us know what a Big Dan carabiner looks like. When I ask for a rigging biner, Big Dan is on its way up the tree.
Joel