Double heterozygous for snow = a⁺b⁺
Normal = ++++

The following are percent averages over a long period of time (out of a possible 16) you get:

4 Normal = ⁺⁺⁺⁺
4 Heterozygous axanthic b⁺⁺⁺
4 Heterozygous albino a⁺⁺⁺
4 Double heterozygous for Snow = a⁺b⁺