It means it isn’t a mutation. It is what original red junglefowl had. They have slate W+W+id+id+ legs.
That wouldn’t work the same. You’d get all yellow leg offspring. (Unless the yellow legged cock carried id+.) The cockerels would carry the dermal melanin gene, but you wouldn’t be able to tell them from the cock.
That's what I am wanting in the offspring is the yellow leg's. I was trying to find the yellow legged buff naked neck's to breed to my yellow legged Aloha, but it seem's that most of the buff naked neck's have those green leggs.