Meet Alva the lab rat! She's a black and tan rat* and works in a lab, obviously! :D
*) Black and tan currently does not exist in rats, which makes me very sad as I LOVE the colouring (hence this character)
Quick pic made using Create-A-Rat: http://kennonink.deviantart.com/art/Create-a-Rat-170224365
Link
Kediil
There are black and tan mice though! That's pretty close!