Steps to reproduce:

1. Tame a horse;
2. Use a diamond horse armor, just to check that the color is correct;
3. Remove the diamond horse armor and put a leather one in the slot instead;
4. Remove the leather horse armor and put back the diamond one

Expected results:
The diamond horse armor is displayed in the default color.

Observed results:
The diamond horse armor color is mixed with the one from the leather horse armor

*Happens to other types of armor as well.
*Reopening the world fixes it.