With hatchery stock, the differences are not so clear, especially in the barring, which should be more straight and defined on BRs, but most often is not. I've heard that some folks got pale legged BRs from a hatchery, though mine all have yellow legs, till they fade with the laying cycle (they still look yellow-ish, not white). Doms are the easiest because of the comb difference, having a rose comb rather than a single comb.
Omran, that pullet you posted a pic of with all the pale, almost non-existent barring in her chest area is not a pure BR. What she is crossed with, I dont know, but her father would be the Br and her mother something else, since if her mother was the BR and the sire a different breed, she would be solid colored, more or less. BR sires pass barring to all the kids in some form or fashion.
Usually, if you think you have a white legged BR, it's a Cuckoo Marans or possibly a cross of the two, which would have white legs since white skin is dominant.
I have one BR hen who lays a quite dark egg, compared to my others. Sometimes, it looks like milk chocolate.