What causes stems to turn purple

[ridejeep2005]

I asked this in another part of forum but i think it was in the wrong section.so, Just that, what cause's the stems to turn purple. Growing sour d. Is it just a colder temp that plant is not use to, or can it just be any type of stress? like spraying azamax at to high of a dose? thanks and lots more ? to come

 

[greekpatch]

yea most of the time its just from cool temps more than likely when the light turns out the temp is dropping by 10 degrees or more