Disney's The Wise Little Hen was released in 1934. It's in full, nice colour.
But Donald's next appearance, or at least the first time he is more like Donald Duck as we know him, is in Orphan's Benefit from later in the same year, and this time, it's back to black-and-white!
What would make Disney go full colour only to then revert to black-and-white?
It's not like the first cartoon was some kind of spectacular, super-high-budget introduction of Donald Duck which made them go for colour. He seems to just be a throwaway "lazy duck" character, just like his pig buddy who never became famous unlike Donald. Our duck just happened to become popular later. So that doesn't explain the high production value for that particular cartoon.