Will the temp fluctuations affect the outcome of the plant (potency/ yield)? Ive got my room dialed in like a swiss watch! 78 degrees constant !
Yes, it will affect the outcome. The cold temps do a couple things. They slow the growth (but by the time you're doing this there's not much growth left anyway, just ripening). The buds get denser. Yield is slightly affected, downward. Time to harvest is extended a bit. Otherwise, not much difference. There is anecdotal evidence that the low stress of the colder temps increases potency, but I have not found that to be the case. It does produce prettier buds, though. I do it the last two weeks, mostly because I'm bored waiting and just want something to look at.
I agree with Boogie. The changes are only cosmetic, and if you're going for bag appeal it's something you might want to do. Many home growers like to do this, and take some pride in pretty nugs. Commercial growers are more about getting maximum yield in minimum time, and getting the product to market as fast as possible, so they don't tend to do much of this kind of thing. Some purple is just genetic, and if you want purple you might try some of those genetics next time around.