I'm not a grower so I don't want to blow your thread up but I'm curious too.. Could they be malnourished, under-watered? (quick google search said maybe water deprivation)? White specs look like mites maybe to me though-- could be wrong, probably am
Looks like mites. Also, is that evidence of you misting plants in flower I see? If so, I'd stop that.
Cold temps or genetics cause purpling. It'll be alright, nothing wrong with it other than the mites. For mites get some insecticidal soap at walmart or wherever you go and spray the bottom of the fan leaves. Don't get it on the bud. Makes the bud taste shitty. Lol
Water your shit or check the nutrient levels I'm pretty sure.. google dark marijuana leaves: http://forum.grasscity.com/indoor-medical-marijuana-growing/26497-my-plants-leaves-have-become-dark-green.html