What is "undefined" colours

[Deborah DeMaere]

Greetings!!

I am curious.  In my attempts at learnng my gerbil genetics I have
been using the gerbil genetic predictor to see what colours mixing
with colours would rend.  What exactly is an "undefined" colour
(as an example aa CC efef gg pp spsp)?  Does it not exist at all or
does it a colour with unusual recessives or ???  I am just trying to
understand what to expect in litters and "undefined" doesn't help
me ;)

With a smile,
Deborah