In my Bantam Marans they are a white legged breed, I had 2 different Roosters I am using, one is Cuckoo from Trish Foss lines, and I only used that Rooster with 2 Bantam Black Copper Hens that are also Trish Foss line birds, I got split gened chicks for gold and silver in my F1s and that is where I am with them now, I have to breed my F1s together to hopefully get the Black Coppers and Birchens as well as Golden Cuckoos and Silver Cuckoos, at any rate out of the split gened chicks I hatched out 8 chicks with yellow legs, I waited until they were over 4 months of age to make sure the leg color wasn't going to change, I got told in the Marans the yellow legs are recessive, so one hen and one rooster both have to carry the gene for it to express itself in the chicks, now I am getting ready to test my breeders, and I know its in the one Roosters line and at least one of the Bantam Black Copper Hens, for these to test I got told to get a yellow legged breed and breed to my birds, mark the chicks from each bird, any that show yellow legged offspring is the hen and rooster that carry it. I got Bantam Welsummers for testing with because they was close to the same size as the Bantam Marans. So in Marans the yellow leg is recessive. You can use a recessive with a non recessive and they say it passes at 50 percent, which is what I'll do because the Bantam Marans gene pool is so very limited, then I'll test the offspring also to see who got it and who doesn't carry it and use the ones that don't carry it for breeder birds, its quite lengthy and I see it as the only way to salvage as much of the gene pool as I can and to get it cleaned up. All mixed breed chicks will be culls but will give me the results I need to know for future breedings.
There must be some test for also testing for the slate legs like there is for me testing for recessive yellow. I'd think if you bred to that Rooster with yellow legs and got Slates legged birds from him, that you would want to test the offspring and get rid of it at that point, which is what I am doing with the Bantam Marans.
Hope this helps and wish I knew the answer to your question, I know I got some Partridge Penedesenca chicks earlier this year from Meyers and their leg color wasn't right either and I had yellow legs in them also, and I got rid of all of those chicks after they turned over 4 months of age, I have the Black Penedesencas and a pair of Crele Penedesencas I'm going to be working with and decided I didn't want to mess with the Partridge ones that had leg color issues. I was able to get a Black Rooster from Denise and am thrilled with that Rooster, now I can start breeding Blacks in the spring.
Victoria
Then I'm also raising a flock of Bantam Welsummers to keep