What stage of growth is the plant in would be my first question. If purple is common on this strain then I don’t see that as a problem. Don’t think it’s over watering either. If your temps ranging from 65-80 f degrees then rule out temps. Plant could be locked up. Did you inspect for mites or any other type of bugs. Do you see any? What are the ppm and ph runoffs? If run off numbers are off you prob locked her up and will need to flush and let soil dry up
Would need to know all that before we take it further and start moving to viroid problems. The main branch looks weird to me. The way the nodes are growing so tight. I’m suspecting right now but don’t want to say it yet. Post side pics of the branches.