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Ur flower is purpling

Your plants need nitrogen for the first 3 weeks of flowering and then they need calcium and magnesium around week 4-5 to build buds and cell walls. Your plant is depleting it's cal mag right now trying to build cell walls which are buds. Keep this in mind for the future. Nitrogen for the stretch week 1-3 Cal mag for bud growth week 4-5 Pk for week 6+

Magnesium deficiency In flowering you can add Mag+Sulfur instead of Cal+Mag

Yes, burned from long term over feeding.

looks fine, look like the genetic you can see the color also on the area where the stem connect with the leaf 🍃 , if it was cold you will see it on the other plants. so just keep them warm, and keep the good work they look healthy 😊

is it a red/pink hue? if so that's senescence / fall colors -- could be genetics or 68F and below temperatures at night. if not, would want to see a bit more progression or other info as interveinal symptoms are not discete to one cause.