You lost me here.With silver, the resulting bird would be mostly white, and that seemed like a lot of work to make a white bird.
Why do you say it would be mostly white?
Your terminology is different then mine....
extended black (eb) Extended black to me is E
Copper Marans are an example of eb Copper Marans are Birchen to me (ER)
E (wild type, chipmunk chick down, AKA BB Red or Partridge)
Wild type to me is e+ & Partridge is eb
Welsummer and Legbars are wild type e+ in my understanding.
I'm confused by your post