…their hair (either intentionally or unintentionally)

Greg Brady, Kimberly Drummond, Laura Petrie for starters. Who else?

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On an episode of My Three Sons, Chip Douglas intentionally has his long brown hair bleached to practically white. By episode's end though, it is cut and returned to its original color.

This one is a little different, but still noteworthy:

Ben Cartwright on Bonanza: For flashback episodes showing Ben as a younger man, Lorne Greene's white hair was dyed dark brown / black.

Donna on That 70's Show

Martin Crane on the episode of Fraiser, where Roz goes into labor at Nile's party.

The entire cast of MASH dyed their hair and uniforms red for one episode.

Donna Martin ( Tori Spelling) on 90210 with her signature bleach blonde hair, dyed it brown at one point in the show . Didn't suit Tori , glad she went back to blonde even though her " natural" hair is dark , she does blonde well!

Archie Bunker dyed his hair to look younger for a job promotion.

Archie Changes His Hair For A Job?! | All In The Family (https://www.youtube.com/watch?v=s1FtjT3A2r4)

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