I have a Houdan roo, that has sired "bator" chicks with hens of a variety of breed, in kind of a 'barnyard mix-match'. He is a good mix of white and black mottled feathers, not on the dark colored side. I have produced RRR, NHampshire, Gold lace wing wyandotte, Buff orph, Leghorn, Phoenix, and Seabright bantam X Mottled Houdan. One thing i have noticed is that the majority of his chicks turn out very dark, if not pure black (a beetle green shimmered black). Many have purplish bars against the greenish-black. I even had an almost pure yellow chick, that ultimately turned black (she is the spitting image of my Austrlaorp). I did a winter batch of 22 eggs, which lended a 100% hatch rate, and only 7 chicks are mottled, or white marked, and the rest are mostly black. Interestingly enough when i cross him with a White Leghorn, the chicks are almost pure white, with three to five mottled feathers, and a very tall feather headdress. I have hatched appx. 30 of his chicks and they all develop the extra toe, the flared nostril, and the tufted feathers on their head, but they do not all have the Y shaped comb. I have had a few that look like your little guy's pics, i believe they are from my Wyandotte. They are a mottled cinnamon color when they are chicks, and they mature into black background with the brown barred wings, and brown markings around their necks. I agree that the shape of your guys head is not indicative of anything i have seen produced by my Houdan roo. The poster that suggested that there might be impurities in the bloodline has an interesting hypothesis. I have some chick pics from the big winter hatch, as well as pics of them now, at 3 months old, if you would like to see them. The females are very docile and sweet. My purebred Houdan roo is also well mannered and tame, and takes very good care of his girls. Good luck with the chick, and good thing you found it a nice pet home. I actually had two Houdan roo's, and i drove one 6 hours away, when i bought my new puppy in February, and gave it to the breeders sister who raises chickens... lol. I just wanted him to have a loving home - and one crowing roo is enough for this little farm!
