Horses and Llamas, including trader llamas, have messed up textures. This started after the 1.19.20 update. Wild horses flicker wildly from their coat color to solid black ( which could possibly be a seizure risk in those with epilepsy ), and appear all white when armored. Llamas ( trader llamas ) appear red and green. 

You can recreate this issue by spawning a horse, llama, or trader llama in the newest update.