I don't think I'll be able to figure any more out, so there's no point in doing that unless you want to, or if it will help someone else figure something out.
I do see that the red isn't even all over. I can't decide whether it looks more like stripes or dots or stipling to me, and I don't know what causes it. It could be some gene, or even something as simple as feathers growing at an uneven rate (which can cause the pigment to be distributed unevenly.)