Yellow and purple leafe tips

Needs more nitrogen easy fix, sativas use more nitrogen than indicas. Don’t g

I think it's needing a bloom formula now it's in flower. Not sure what your nutes are that your using, they may have the wrong NPK for flower.

Npk, calcium, sulphur and magnesium. The 6 macros make up 99% of all nutrients a plant will use. The other 7 iirc make up thay last 1% but are none the less vital. The stems have nutrient highways called xylem and phloem these highways are responsible for traffic. Nitrogen and potassium both share the same major highways, makes sense being most uses. During flower in a perfect world you want nitrogen to run out within the soil and the plant to cannibalize pre existing nitrogen elsewhere in the plant. During flower once there is little need for nitrogen you want that nutrient highway 99% potassium. Everything other nutrient uses secondary small side channels. The entire cure is about ridding the plant of as much chloryphyll as possible, true masters dial in their nitrogen content to the gram. Hope it helps with understanding.

Nice she is showing good bio chemistry within the leaves, senescence is the process of the plant beginning its "death spiral" so to speak. The reallocation of nutrients within a plant's leaves. Some nutrients are mobile some are not. Nitrogen is mobile meaning once nitrogen runs low the plant will start to cannibalize the mobile nitrogen where it is needed elsewhere for more critical bud development. Chloryphyll itself is composed of nitrogen with a magnesium core. This is the yellowing you see. As chloryphyll is removed the other pigmentation remain, this will show through as purples (anthocyanin) or red/orange (cartenoids). It is a sig of a healthy grow done well. Good job. Cold night temps should help if you choose to bring out more purples, but don't push it wait till you are deep into ripening then slam it low see what happens. Good luck.