Correct, it's not black or neutral. The color is very similar to what I get with green tea, which hardly discolors the paper at all.
I might not be remembering correctly, but I think I read that the problem with gall inks happened when ferric sulfate was used as the source of iron. Small amounts of sulfuric acid are formed which the eats away at the paper. I think gall inks that used a different source of iron, like ferric or ferrous acetate, or just exposing the gall ferment directly to iron, have been more permanent. But that's just from my memory so best to read the sources!
Happy New Year!