I hear what you're saying, and I totally respect that. I certainly haven't been around long enough to merit a worthwhile opinion on it!
I do have a lot of experience with horses, though, and it doesn't bother me, personally, to bring outside blood into most breeds. I know some people and some registries have a very purist viewpoint, and I can see that, too. My current riding horse is an Oldenburg with a somewhat unusual pinto color. I believe the pinto gene was brought in by a Thoroughbred several generations ago. I guess I feel that as long as it meets the standards and breeds true...if it walks like a duck and quacks like a duck, then...? After all, weren't Marans heavily influenced by Croad Langshans?
Like I said, I'll defer to your expertise! Maybe my chickens need a new name!
Since it might be the lavender gene of an Orp over the copper of a BCM, maybe Lavender Marington? Or use the the German term for the straw dilute and call them Isabel Orpans, lol? I should start a movement!