Hi 5foot,
I can only speculate, but I believe the orange color on the brookies I catch in this stream is mostly from genetics (and possibly somewhat from diet). On the day I caught this trout I caught seven brookies out of 114 that had a substantial amount of orange coloration. If it was caused by diet maybe more of them would be orange?
I believe the trout are colored-up like this year-round in this stream since I typically catch an orange one or two regardless of when I'm fishing. (I don't fish here in the winter.) I don't doubt that more color is added for the spawning season, though.
This may surprise some of you, but I believe the orange-colored brookie in the photo is a female. It has no hook-jaw. Further evidence that it might be a female is that probably thirty years ago I kept an orange-colored 7" native brookie on this stream due to deep hooking (hey, unfortunately it happens). It was full of eggs. Of course, maybe that one was just a male that identified as a female. 😉
I don't recall ever seeing a crayfish in this stream, though it is quite possible some are there. I doubt there are many, though.
I don't think the water temperature has anything to do with the orange coloration. (You probably don't, either)
I also don't think it has anything to do with males that didn't spawn the previous autumn. (You probably don't, either.)