They are basically an overlaced plus shafted version of brown red, with the gold portions a couple of shades lighter than brown reds. Genetically, they are the gold version of Silver Sussex.
I've always wondered why silver Ameraucanas were made on the silver duckwing pattern instead of birchen like silver Sussex. Was it just a personal preference kind of thing?
Here again some terms we use have more than one meaning.
When it comes to varieties "silver" and "silver duckwing" are similar, but different as Mike pointed out.
When it comes to e-locus "duckwing" is used interchangeable with wildtype (e+) and the males have a silver or gold wing triangle. Birchen (the e-locus gene, not the variety) (E
R) is often referred to as crow wing and the wing triangle on the males is black or the ground color of the bird.
Mike pointed out the difference to me decades ago at a show, where I had entered what I thought was a bantam silver but since he didn't have the silver/white wing triangle he was really a birchen (the variety that is based on E
R).