The yellow ones are sometimes sold as green BN's (dont ask why - colourblind LFS assistants me thinks)
I had one or two yellow yellows in my first brood - not sure how many will be in my recent brood
Perhaps yellow is a midway to albino?
Anyway - I know my two are not identicle species of BN so my fry are hybrids and I suspect mamy BN's in shops are hybrids to some degree - anyway - io wont tell if you dont (I happento have no probklems with hybrids as they tend to be tougher than pure strains)