I've had that coloring show up in some of my Purple spawns. I sold some to online aquantainces with the intent for them to breed them so I could get some back. That never happened! Here's a few pics. of them.
From what I understand of genetics, you have to have the Red-loss factor in order to have the color Yellow and they cannot both exist on the same fish. The Bettas in my fishroom don't follow the rules so I guess these Armageddon Bettas don't either!