Since I am not SURE it is E/E that is totally black.. this would be my guess only based on information from elsewhere. E/e^b is Extended Black/Partridge cross. If the children got E from one parent and E from the other parent then they would be E/E.. and I believe that was what the supposition of a totally black downed chick would be. e+ is wild-type - but it doesn't denote partridge although it will throw chipmunk chicks. Its the base for silver and gold duckwing. E/e^b will usually be totally black, but some may have leakage because of other genes present in partridge coloring (its not just e^b/e^b, there's more stuff in there). This is something I am still figuring out myself.. maybe somebody with good genetics will come in and answer it...