Yellow leave with Purple tint (about 5 weeks in flowering.)

http://imgur.com/mw1Rf.jpg
http://imgur.com/kre3H.jpg
They're mostly looking like that, they're leaves that are coming off of the nodes (i've trimmed all but the top fan leaves) some of the leaves are still green and get that purple tint, but pretty much every day, I have a few leaves falling off (or that I can pluck without pulling much).

From what i've read, i'm told it could be from the temperature getting too low? usually with lights on they're at about 74 degrees F, and at night around 60 or so. What do you think?

yellowing is normal close to the end of flowering,the plant is sucking all the nutes out of the fanners.lookin good

but the purple is the cold air i say,all my outdoor ones looked like that after sep