There are actually quite a few cases where light legs at hatch can turn slate later on. Wheaten Ameraucanas hatch with pale legs that turn slate. Lakenvelders sometimes hatch with pale legs that later turn slate. Dominant white can cause a chick to hatch with pale legs that turn slate later on, as I learned when I tried to do a skin color sexlink cross that, as a result, went rather disastrously.
This is one of those cases as well, because the pictured chick is definitely a Silver Sebright bantam.
