Also something to consider as they feather out is that Sebastopol geese can be fully curly all over their body, some can have curled feathers but be smooth breasted, and some can even be completely smooth with no curled feathers but from what I’ve heard that’s less common as breeders breed for...
White in geese is the result of a gene that dilutes whatever color the bird actually is, so often a white goose can actually be genetically grey or buff but will present as white.
Then there is the spotting gene responsible for geese that are saddlebacked or pied, birds that are splotched with...
There are grey sebbies, it’s possible they’re mixes but just as possible that they’re purebreds with a dormant gene. The grey feathers will be a dilute grey and the black feathers are actually true grey, they just look darker while they’re developing.