So I've been hatching red-sex links (NH/White Plymouth Crosses) for sale locally. That's been working great, and i'm very happy with the sex-link, but... I've been getting a handful of black chicks out of each hatch. Now, the first few times I didn't think much of it because I had an EE rooster that was a yard bird and a few of the white plymouths routinely escaped from the breeding pen. I've since gotten rid of him though, and still getting some black chicks. He's been out of the picture AT LEAST 6 weeks before this hatches eggs were collected. Could his swimmers still be in a hen 6 weeks later? or is there a recessive black gene in either the WP or NH thats expressing itself occassionally?