They wouldnt be considered a subspecies, but a breed, since they are man made. Most emu's or Rheas i've seen were inbred over and over to get the blonde and white colors. Then they took a inbred bird from one group and crossed it to a inbred bird from another unrelated group to keep carrying on the pigment deficiency. Many groups of Rheas had problems with chicks being so weak that they wouldnt live or grow well from generations of inbreeding. I did see some solid white emu's once, plumage was very pretty, but the face's were ugly lol.