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Demi Lovato

JB Lacroix/FilmMagic

Demi Lovato didn't just lighten her locks—she dyed the tips of her hair hot pink!

The 19-year-old singer and X Factor judge debuted her sassy new 'do during a round of auditions in San Francisco over the weekend.

So what did Demi's cohost Simon Cowell think about her trendy tresses?

He loved 'em.

"Yay!! Simon approves of my pink hair!!" the former Disney star tweeted Saturday, along with a pic of the former American Idol judge giving her a thumbs up.

Her 10-year-old kid sister, Madison De La Garza, wanted some credit for inspiring Demi's new look.

"For the record, @ddlovato copied my hair," Madison tweeted (and Demi good-naturedly retweeted). "I did it first… But, you know, blue ;) #ilovemysister"

Too cute. What do you think of Demi's partially-pink hair? Weigh in below in the comments.

PICS: Stars' Rainbow Hair