Sour Kush stem turning purple.

Hey Growmie, Looking at the photos and how you describe it, this is a Phosphorus Deficiency. It generally appears on leaves from the lower/older parts of the plant. The lower leaves may turn dark green or yellow, and start getting spots or big splotches that look brown, bronze, or even a little blue. The leaves may thicken and curl, and the affected leaves feel stiff. Sometimes the stems of the plant turn bright red or purple. The way you fix this is by giving the plant a“bloom” or “flowering” nutrient since it contains high levels of phosphorus to aid in flower production, and phosphorus from a liquid nutrient is one of the most readily available forms of phosphorus you can provide to your cannabis plants. Hopefully, I answered your question and remember and remember ..."Happy Growing" and "Free your mind one puff at a time".