How purple can Purple Kush get? Does cooler air a...

59o F night temp is plenty cold to trigger colors other than green.
You never know how it will turn out. And some strains named blue or purple may not show those colors in all conditions. Cold temps definitely encourage colors we associate with autumn foliage.

Leaf color is curious and novel, but not a genuine part of the psychoactive experience, so don’t sweat it if it doesn’t turn. Enjoy your harvest.