Hard to tell from the pics but it could be normal if it's getting cool enough at night where you're at. Alot of plant change colors towards the end, purple being the most popular.
no its not over nuting, its either from chilly night weather or from a mg deficiency. Probably cool weather because like humans, blood circulation is restricted when cold. the plants should be ok. The purple may also be a strain trait but weather is probably it. Epson salt can help for the def.