I’m not sure how many of you know this, but blond/blonde is one of only two adjectives in English that inflect for gender. Blond applies to males; blonde applies to females. Interestingly, the other inflecting adjective is also a hair color: brunet (males) and brunette (females).
I would be curious whether this same mutation in a male Mallard would have any noticeable effect.
There’s no solid information on whether male Blond Mallard exist or not (that I could find), but considering that they are result of wild-domestic interbreeding, I’d say it’s certainly possible. In fact, I may have found a few observation with male Blond Mallards here on iNaturalist.
As you can see, possible Blond Mallard drakes have lighter plumage and grey or black heads. Females have a more tan plumage. This is comparable to the breeds Khaki Campbell and Buff Orpingtons, seen below: Khaki Campbells Buff Orpingtons