Colts w/"mismatched" parts?

I've noticed lately seeing blue Colt Gov't Models with nickel triggers. I've seen this on .22LR Aces, .38 Super and .45ACP Mk IVs from the '70's and '80's. Was this a "normal" practice for Colt? I've also seen stainless steel Colts of newer manufacture, some with grey and some with black plastic triggers. Was this done on purpose or did Colt probably have problems with their inventory control? What's your take?Thanks in advance for your responses.