It will take six years to unlock all the colors on the Duck Disguiser toy from Noblegarden, Blizzard has confirmed in a recent forum post.
The Duck Disguiser is a toy that allows players to transform into a tiny duck of various colors. This toy, along with a choice of six disguises, is rewarded through a Noblegarden questline introduced this year. Since the questline can only be repeated once per event, this means it's only possible to unlock one disguise a year.
As we've already reported, unlocking a disguise is character-specific rather than account-wide. Characters who haven't unlocked any disguises can place the toy, but don't get an option to change their appearance.
In a recent forum thread, a player asked if this was a bug. Blizzard responded to clarify that it is intentional, and future disguises are meant to be collected in future events — therefore it should not be reported as a bug. The post also directs players who would like to see this changed to feedback/suggestions — suggesting Blizzard would be open to making a change based on community response.