He truly IS a chimera, because of the different leg colors. Yellow legs are the result of a chicken getting recessive alleles from both parents, making a yellow legged chicken homozygous. White legs, however, are caused by a dominant gene, so if a chicken has a copy of that gene, it is the displayed phenotype. Your chicken is a chimera, and one leg has the genetics for recessive yellow, while the other is a dominant white!
