Many breeds come in all KINDS of "non-standard" colors that aren't accepted by different organizations, but just because some guidelines humans made up for breeds doesn't mean that other colors aren't going to come up every now and then! For example, you can get yellow Aussies. And you can get brindle Border Collies. But of course, neither of those are "breed standard"

And working dogs of course don't have to follow the conformation standard, for coat colors anyway