Scooby Doo - Shaggy's Hair
In the episode "A Clue For Scooby Doo", Shaggy sits down on a rock and opens a secret door. Velma goes over and chats with him and then there is a closeup of Shaggy. His hair is blonde!
The episode of Scooby Doo entitled "A Clue For Scooby Doo"