Genetic purple leaves?

Any ideas y the purplish leaves? I over fed 2 weeks ago and haven't fed again. PH is normal as well as runoff. Temps 75-77 during day. 65 at night. Roughly 3 weeks from harvest. This all info I got so if any ideas I would appreciate it.

Probably low night temps. I think 3 weeks aint going to be enough for them to finish.

Colder temps can bring it on and/or genetics. It's quite normal, for example just got done harvesting some which were more black then green.

Looks genetic too me..