hmm purpleness is always pretty.iv'e had it once its most likely just a trait of the plants some spots purple some green i wouldnt worry about it...unless it actually is hurting your plant wich i doubt., my uncles strain that hes been growing for yrs does this every year....and no its not bud rot forming.just purple buds...no biggie.alot of strains these day are crossed bred with plants that purple genetics that could be it also...or its just lovely new england weather where we get those fast cold spots during the night...just go relax by ur plants at night and see if you can feel a very cold breeze...