I can help you with mixing Buff. I know quite abit since I've been working on a Wheaten Crele Orpington project, & it includes Buff Orpingtons, Barred Rocks, & Australorps.If I can get home before dark, I'll try to get more. I'll try to get pics of the siblings too, but they are so darn flighty. so far there has been no color leakage whatsoever. I've gone waaaayyy down the rabbit hole reading about barring genes, but there's just no info on mixing a buff chicken with any other type of chicken.
Here's Dino's mother tiger. She's a Buff Orpington/Australorp cross.