Gosselaar Had To Dye His Hair Blonde For Every. Single. Episode.
The creators for the show always intended for the main character, Zack Morris, to be a pretty boy with blonde hair. That was a problem when they hired Gosselaar, who is a natural brunette, to play him. Gosselaar admitted that they’d dye his hair blonde for every single episode because it would wash out so quickly.
The continuous hair routine was so bad that Gosselaar once remarked he was surprised to have any hair left by the end of the show.