Yellowface Skyblue Type 1 - Heterozygous Homozygous (Double Factor Yellow Face which is visually white)
The heterozygous Yellowface mutant 1 is the exhibition form of the mutation.
There may be a slightly yellow wash in what would be white areas of the wings and tails, but the less there appears, the more clearly defined is the bird.
You can have this yellowface in Grey as well as in all others varieties.
Information from PHT Budgerigars