I think there was a link earlier, but I stumbled across this page today --
https://www.theverge.com/2020/3/31/2...yourself-bread
My mom had an "Old Timey" Alaskan cookbook and I remember there was rhyme/mnemonic thing about the colors of mold on sourdough. Sort of the thing like with snakes, Red meets Black/Friend to Jack, Red meets Yellow/Kill a Fellow, but about when you could keep a starter or start over. Did a little searching but haven't found it yet. Finding lots of interesting things about mold -- except that I have rather an aversion to it myself.