Belated thank you, I think I get it! Separated lines on the gold/silver base and extra melanizers for the E^R based birds makes a lot more sense than where my brain was trying to go with it, it was trying to needlessly over-complicate it.
So I've recently come across the AA & their theory on using birchen/crowwing to produce blues with better lacing; This thread on the E-locus is super interesting to me, but I'm middling at best with avian genetics, so I'm not as positive about how exactly they are achieving the completely blue...