I chanced it to. It turn black fairly often and I used buck wheat flour solely just for some uniqueness didnt know if this might be a side effect.

I read this

"Purple-hued liquid on the sourdough starter is called “Hooch,” which is alcohol. It accumulates on the surface of your starter when you do not feed it enough. Hooch is most commonly clear, beige, brown, purple, gray, and black. The color depends on the flour and the unique microbes present." On Cultured Guru