I'm betting he's a mix, hope David will respond to the picture just posted, leg color looks close, not having the White earlobes is what I saw right off the bat. The Black pullet definately should have those white earlobes even if she's a mix, have you saw this womans egg color? If all you're looking for is the dark egg color ask her to see her eggs. As for them being pure I don't think they are, not a bad price for a bird if you're satisfied with them and they are healthy, finding healthy birds can be a real issue and finding ones that have been tested for diseases is another issue, I'd ask also if she's innaculated them for anything some do Mareks. Most of the other diseases they don't mess with the Innaculations, and its just a given here in the States that you will get Mycoplasmas as they say that is in 75 to 90 percent of backyard flocks and passes to the eggs, so it keeps on going as carriers. I'd look them over real good, remember what is in her flock will be in yours when they come to you. Ask to see her breeders, and ask her what she does when birds get colds, that will tell you if she has had any issues with their health and will answer the question on respritory diseases in her flock for you. You can treat for Mycoplasmas, if its Infectious Bronchitis, it won't work for that, but there is an Innaculation for that, the trick is the Mycoplasmas have to be under control first to use the Innaculation otherwise you throw them into an epedemic state and the Innaculation doesn't take effect. Just be careful and ask alot of questions. If the Black one is pure and has the lobes to the back of the comb and has good egg color it should pass to the crosses created using just something like a Gamefowl Rooster, I've saw crosses eggs that were dark, like a 7 to 8 on the Marans color chart, so you could get some dark eggs producing pullets from the cross. I think the more generations away from the pure ones they possibly loose those white earlobes, not 100 percent sure on that and wish David would comment, he is very knowledgeable about breeding and has written a book on genetics in poultry, so I'd go with what he told you about which one is the Crele patterned bird.
Victoria