[or reverse it for Heterozygous axanthic]

Double Heterozygous for snow = a⁺b⁺ X Heterozygous albino = a⁺⁺⁺

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

2 Normal = ⁺⁺⁺⁺
4 Heterozygous albino = a⁺⁺⁺
2 Heterozygous axanthic = b⁺⁺⁺
4 Double Heterozygous snow = a⁺b⁺
2 Albino = aa⁺⁺
2 Albino Heterozygous for axanthic = aab⁺