Purple top stems.

Purple/red stems and leaves happening in a non purple trait plant is usually a sign they were not being given enough feed. This is my signal while the girls are veging and I see the stem of the leaves starting to turn a little purple/red then a 50 to 100 ppm increase in food follows that. This is only while girls are veging. Non purple trait plants can and usually do show some purple/red in the leave stems while in flower. Cheers

Hi mate....nice baby!!!!😎 There are countless strains of cannabis on the planet, and some of them are capable of developing incredible pigmentation. So is quite normal... Don't worry and keep going💪 Good luck with your grow mate!💪💪

Check out: https://www.royalqueenseeds.com/blog-should-you-worry-about-purple-or-red-cannabis-stems-n1311

Mag Chloroses. Many factors. Light too close/too powerful, and/or overwatering, or first symptom of a Mag deficiency.

I believe that a purple stem is usually a sign of stress... I could be wrong though 🤷‍♂️