That type of leakage can be bred out by introducing non leakage speciments to the flock or by breeding males that dont leak with their mother or sisters
Egg laying trait is a Polygenic trait. So males transfer their sex linked genes(likely 2) to their doughters. Now I calculate that the total genes involved is about 20 since the reciprocal cross difference is only 10%
Sumatras as we know them are an American breed. They are Extended Black with Melanotic and Pg(Pattern Gene) due to the Ml-Pg linkage. Extended Black birds will deposit a layer of dark epidermal melanin to the shanks and that is further compound by sex linked dermal melanin enhancer id+ so there...
Melanotic and other melanin enhancers tend to Darken chicken eggs, Diluters like Barring, Dominant White and Sex Linked Id makes them Lighter.
Birchen is the second most melanized e allele and when not Diluted by known diluter it will have dark eyes
Of the many peojects that have come to my mind is this and you seem to have done it right. Orpington and Cochin are about the best breeds. I believe Brahma are too tall and not round enough
Whiting True Blue/Green are not a stablished breeds, they have no standards, they are bred to be very good layers of colored eggs and as such can have all sorts of e allele chick down