slate vs. black

[Lanie McWilliams]

How do you tell the difference between slate and black?  I have a young
gerbil that I just don't know if she is slate or black.  And if she's slate,
then that means both of her parents carry a recessive g, right?

Thanks!

Lanie
Royal Star Gerbils
http://www.angelfire.com/ks2/flamingblizzard/gerbs.html