Yes, colder night time temps will help bring out a plants coloring, no colder than 50 F, if it has the genetic makeup for it. Just cause you have Purple Power, doesn't mean you have a purple pheno. Now it doesn't have to be cold for the purple to come out, but it does move things along if you have the option to do so. I've always considered giving my purps 48 hours darkness before chop in a fridge, but don't have the resources right now.
Also, the coloring usually doesn't develop for most strains till late flower, so you still may have the purp.
Good luck in your quest for purple, hope you get lucky on this one. Grow well.