Dark Purple Coloring Branch Base

I also have purpleing on my Blue Cindy plant I'm growing out right now, and next to it in the same tent I have a Maltezerz with no colouring on it, they are by the same breeder, G13 Labs. I feels its all about the genetics and that some lights will express this trait more. I think that LEDS be them full spectrum have spikes in the blue/red range and this is what causes the streaks to be more evident on indoor grows, I would not be surprised if this is also linked to light intensity and how close the diodes are to the plants. I don't have any stains that I have grown indoors and outdoors to fully test this out but I would not be surprised if this is part of the case. I view it sort of like how some tomatoes will blush blue/purple or more red/pink if they are exposed to full sun on that side of the fruit. I notice apples do the same thing but its tends to be deep reds or pinks that get expressed on the sun kissed portion vs purples. Given how locked in you have things I do not think this is at all any PH stress or imbalance in nutrients. I don't know what bearings internally tend to make the plant express this. Both the ones I'm growing are Sativa dominate but the blue cindy is growing more like a Indica phenotype so who knows. I have heard that strains that are known to go purple or have fruity sents in its lineage are more likely for this. but its not scientific in any way. just anecdotal. Over all it looks to be healthy and I would not put much thought into the whys. This will follow though into the petioles for my plants that I have noticed this on. I also let my plants get quite chilly at night down to 16c and up to 28c in the day. this maybe another factor. Good Luck!