One of the standards that breeders breed for is the color of the legs. The Standard of Perfection put out by the APA describes in very specific detail what every aspect of each breed is supposed to look like from the color and shape of the comb, the coloring of the feathers on each part of the body, the shape of the tail, the body shape and size, et al. One of the standards is the color of the legs. It takes very careful breeding to produce chickens that are even close to the SoP and even if the parents are close to SoP, that doesn't mean all their offspring will be. If you were breeding show birds, adherence to SoP would be crucial.
Most backyard chicken owners aren't SoP savvy and they really don't care. The producers of chickens meant for the backyard flock just put a rooster with a hen of a certain breed and sell the offspring. As a result, you end up with chickens of the same breed that have different color legs, or the coloring on the feathers is a little different, or the body shape is a little different. For a backyard flock that will never see a show ring, it's perfectly okay if the chickens aren't SoP.
So yes, it is fine that your chickens have different color legs. There is nothing wrong with any of them.