Intesting. I have 2 colonies as well.
Colony A is normal pieds (?) pink ears clean butts.
Colony B is 2 female gremlins (1 normal, one albino/muted) and the male is normal pied dirty butt, black ears.
Colony B produces higher numbers per litter, however colony A produces every 21-25 days on the nose. BUT Colony B is younger.
So that's my experience, sort of the opposite of yours...

.....Mike?