The yellow on the bottom of the feet are similar to my BSL but I crossed them the most common way. I used a New Hampshire Rooster over a Barred Rock Hen. My pullets are only a little over a week old and they already have some red tinting in the neck line. However, both colors of sex links have quite a color variety. This is due to the fact that there are several different breed combinations that produce color-sexable chicks.
One of the many combinations for the Black variety use a Silver Laced Wyandotte Rooster and A White Plymoth Rock Hen. They are sex link but unlike the more common varieties, this hen has silver in the neck rather than the more common red tinting.
YES IT IS A BSL AND IT IS A PULLET
Try and remeber that Sex-Link does not descride a breed but a typ of sexing done at birth called "color sexing". The hard truth is that all sex-link chickens are not pure breeds but in all reality they are mutts. They each come from combing one breed of rooster to another breed of hen, based on genetics, that produce a noticable color differrance between day old male and females.