I am not sure there is an official list per say. In that I mean I don't think it has been studied scientically for someone to say this is how they must be written.

Here are some of the common ways I have seen it written - but if this is for your use then you could use whatever "codes" you wanted to.

NN = Normal wild type
aa = Albino (so Na = Het albino)
CCgg = Orange Ghost
ccGG = Carmel
Np* = Pastel (*= codom)
Nm* = mojave

The below I haven't seen anyone really use but they would make sense to me based on the above ones.

Nl* = lesser
Nc* = cinny

Hope this helps,
Sean