Leaf becoming a little purple

It can be quite normal, even almost black leaves are possible. As Southofheaven said, usually caused by cold temps at night or a genetic trait. There are some pictures of nearly black plants in my diary "cannabis conundrums", week 7. They are only small plants, but were grown outdoors mid winter as a "fun project", some leaves were frostbitten, but otherwise they just sat there under the eaves and unprotected. Interestingly, the inner and lower parts of the plants stayed green. Hope this helps,........ Organoman.

Awsome thanks! Even before flushing?

Either cold temps, or genetics 👍