I was messing around with horses on a superflat world. I gav a black horse enchanted iron horse armor with thorns 3, respiration 3, and protection 5. I removed the armor, but all horses of the same color combination still appered to be wearing iron horse amor. Horses were black with white stripe on nose and white markings on their lower half of their legs.
Does MC-16264 describe your issue? Was the original horse glitched as well?