I am not an expert at genetics but I think if your offspring doesn't have a bib or show the runner pattern (both are incompletely dominant according to Storey) then if would be from the chocolate drake and the blue fawn hen. If so, she must be female
. Here is a link about the genetics: https://www.backyardchickens.com/articles/mallard-derived-duck-color-genetics-basics.74277/
