Hi pumpkinpie + Robinia,
Well you can knock me down with a feather!!
We used to have silverfish in and around our bath (when I was very young), and were lead to believe that they ate the plaster etc from the walls...Never saw a black one, always a light silver in colour (probably too shy to come out until they were in their refinery! lol)...They certainly scurried about, and I used to hate them...Think that if you do see a silver grey one pumpkin, you will see the tiny scales with the naked eye (as we did) - it is probably because of the dark colour that these are not so visible..