I do not know if there is 'something' in all yellow legged Leghorns, but in my experience there must be something in yellow legged black Leghorns from England. I have a black hen with very yellow legs. When crossed to 'ordinary browns', her daughters' legs go dusky(as if it was recessive). Can anybody else confirm this observation?
Yes, had similar results crossing yellow-legged black Jap roo (Id/Id) (ER/ER or E?) to Jubilee Indian Game bantam hen (wheaten, I/i+, Id/-). But the daughters weren't dusky, they were very dark legged (including I/i+ het. Dominant Whites). The sons were darkish/dusky when juveniles & ended up clean yellow-legged.
Fred Jeffrey (Bantam Breeding & Genetics) noted similar with Cote's study, with a cross between a yellow-legged Blue Frizzle Cochin (E/E ml+/ml+ co+/co+ Id w/w, * didn't distinguish between E or ER in this study) roo x Brown Leghorn hen (e+/e+ Id/-) where offspring had 'willow' legs.
*It's probably a sex-influenced trait, not sex-linked.