Gerbil Colour?

[Ubu Noir]

Hi, just a curious side-question during all this colour talk.
When i bought Key, she was really small, really still just a baby.  One of several reasons why I picked her out as a friend for Spoo was her colouring.  I thought that since she was so young, her colour would change.  I've had her over a month now and she's still the same odd colour.  She's the same Agouti(?) (generic gerbil-brown) as Spoo, but she's got a PURPLE cast to her fur!  It's sort of her under-fur that is purple, but in the light she's more purple than brown.  So, is this just a different brown, or is this another specific colour of gerbil?  Just wondering,

Thanks,
Kelly Moore + Spoo & Key