Lost hair comes back brown not white

Has anyone had this happen? I’m using fin for MPB (obviously) but I noticed the other day, a hair I lost was part grey at the end, and suddenly turned black about halfway thru up to the root. And I just brushed this off, but I noticed the same thing on a couple of other hair today again too. I know for a lot of people fin darkens their hair. Mine is already pretty much black or extremely dark brown.

The change back to the original color may reflect reversal of miniaturization in some white hairs. This means that the drug is working. Not a usual finding however.