It sounds to me like two mutations. The recessive blue one and maybe the male carried a second allele that combined with the blue allele would create this splash? It seems unlikely to have two spontaneous mutations happen at once…
Wow! Just discovered this thread, looks like a spontaneous mutation. Interesting how it lets the phaomelanin show through, I haven’t seen a gene like that in ducks. It reminds me (sort of) of dominant white. Also, that is the most bright orange I’ve seen on a duck. Buffs tend to be more fawn...