Ive ridden a 16.2 80% foundation App that was red turned grey/white and has minimal mottling. He was a nutty horse, but all App.
Im currently working with a 16.2 solid red mare, not a sign of App at all; no mottling, no spots, no cap, nothing. She isnt even built like an App, she looks like a warmblood TB cross with forearms as thick as my thigh and what a neck shell have when she gains all her weight back. Smooth mover too. But her papers say that she is half foundation App and half Appendix, and her last baby was LOUD App coloring, a black leopard. She was being used to breed for colored sport horses. Supposedly solid Apps throw really loud colors in their foals, and Ive heard the same thing of solid paints too.
Think of it not as a failure but as a success in how not to do it.
Don't look in a horses mouth for a gift.