Leaves turning purple/ jack herer auto

I think this is down to a genetics thing. My blue jack (blueberry x jack herer) they all did the same thing. Temperatures can also play a role in purple leaves. It’s probably also down to being maybe a bit hungry. Weed tends to consume fan leaves to keep promoting flower growth. I wouldn’t try to change much. Just maintain environment and a good water/feed regimen and ride it until the end. Sure it’s more desirable to keep leaves nice but a few fan leaves getting dickered isn’t the end of the world. It’s also a good opportunity to defoliate the leaves that go south. Your plant looks great. Don’t stress too much. As long as the buds are forming nicely, you’re all good. Cheers 🤙