Iso picks up chlorophyll more easily than any other regularly used solvent. From yellow to dark green depending on how ground up the material is or how long you let it sit. But not sure about colour changes under heat actually, pretty sure when I leave cannabutter on for a longer time the colour of the water changes from a darker green to almost black, either terps or chlorophyll, cannabinoids aren't (very) water soluble, no discernable amber though, unless it's purple bud.
I dunno, I've seen tests on cobbed buds in icmag that were all amber trichs, mostly thca, no significant amount of cbn, but also, my memory is hazey I've found, lol. You also see it in sun dried cannabis, lot's of amber trichs, usually only let out for a day, two at most. No way that's all decarboxylated or degraded. But even a small percentage of degraded/decarboxylated cannabioids could possibly lead to a significant colour change, hell if I know. I'd just venture to guess that terpenes are much more volatile and a more likely culprit.
And then I read it's actual distillate, oh, I just assumed you had some jars of iso with bud you rinsed out. Carry on, lol.