There is really nothing much to do with triggers and hammers. Any abrasive material will adversely affect the existing case colors. I would simply wipe the parts down with acetone and oil them up. Case colors can be redone by experts in this field of work, but would be expensive and not worth the cost for most revolvers.
The above poster is righ on as regards Case Color care. Case color is only .001-.002" and is very easily damaged. Acetone will remove any old dried grease or oil and should be followed by oiling with a good gun oil. Re-case coloring runs approx. $75.00 per item and is only cost effective on rare parts like Registered Magnum hammer & trigger. Doug Turnbull is the recognized expert when it comes to case color.