Too hard to tell if that bird has blue dilution from that pic, but possibly so, & if so, likely homozygous? Much white = those gene combinations that may help your duck express phenotypically as such. The bird isn't dusky (facial pattern). Wild-type mallard (M+) + light phase (li) + blue dilution (homozygous) = Saxony. This bird has more restricted pigmentation? Yes, possibly restricted mallard as opposed to wild-type! Light phase?? Harlequin phase would wash pigmentation out more, plus maybe extend claret onto the shoulders as evidenced (although light phase will do that also)? Wild-type mallard + light phase minus blue dilution = trout & that bird isn't trout! To me she looks like a restricted Saxony, therefore, resticted mallard + light phase gene involvement possibly? (& possibly blue dilution but I just can't see from that pic). Likely impure @ one or more Loci.
Now it is late here (Australia) & I'm tired & not thinking clearly
Cheers