I always thought tetrach spots were like the the reverse of bend or. Where bend or is over pigmentation of the hair - tetrach is depigmentation with no loss of color to the skin below. White hair/dark skin. There were a couple of Spanish type horses in Tx that had areas where the skin randomly depigmented in small spots at different places on the body not so much the muzzle or sheath area. Wet they had an odd look because the spots showed up really well.