So I guess I am really confused about why you are saying that Birchen is a color and it can only be Silver and then you say a Gold/en Birchen is a Brown Red? It appears that these two terms can be used synonymously.
You are basically telling Chickenextreme they are wrong about saying the bird is a Gold Birchen color but then you say a Gold Birchen is a Brown Red and then go on to say is can be a color and a pattern both. What if Chickenextreme is referring to Birchen as a pattern and giving it the adjective Gold, and you are saying that the Color is Birchen because by your definition the color Birchen is only Silver and if it is the pattern Gold Birchen you only want to refer to it as a Brown Red. The link you provided calls the color/pattern Golden Birchen and only parenthetically qualifies it as Red Brown. This is why it is so confusing.
It seems y'all are arguing apples and oranges. But are both talking fruit.