Why is one of my plants turning purple at the top?

Hey Growmie , This is not bud rot. It looks like the normal autumn colors the shows when its near harvest. You can tell it's not bud rot because bud rot attacks a plant's stem, which will appear mushy and gray. As the infection progresses, signs of bud rot are characterized by wilted, yellow, and burnt leaves. It's tricky to spot bud rot ahead of time because the fungus first takes hold inside the plant and works its way to the outside. Hopefully, this was helpful and remember ..."Happy Growing" and "Free your mind one puff at a time"