There's a post I'm not done with yet but it explains a bit about the canine races. Foxes along with cats are two of the few races that are physically androgynous. However, if you want to tell what the gender is of a fox or any other species; look no further than the neck. ;) it can give a lot away.
Needless to say, Tails did not inherit his father's eyes. :D And as another side note; Amadeus' brother and he are identical twins. Except for the fact that Merlin has a mole on his right cheek.