I'm pretty sure it could revert back to blue after the bleach, but I'm wondering if it is inert after the tannin. I've reversed the color after using alkaline bleaches such as borax, ammonia, D-76, etc., so I think washing soda would be similar. But, I've never used tannic acid and so I don't know if that makes it inert.
Thanks for any update.
Now I wonder if the tannin stains, or tans.... it certainly produces a different effect than coffee has for me.
Now as it's up as an article perhaps a mod could lock this thread and move the discussion there.