Dyeing to win an Oscar?

First Lindsay Lohan crossed over. Then Britney Spears followed. Now Cameron Diaz is into it.

Why did these three go over to the dark side, dying their lovely light locks and/or natural red hair a deep brown or pitch black?

There are several reasons why an actress opts for a color change. It can be a frivolous personal decision. But more often than not, it's a serious career move.

The fact is that brunettes are perceived as more intelligent and more intellectual than blondes. Go ahead think of a funny brunette joke. I rest my case.

That's why blonde hair sometimes sends the wrong signals for an actress. Brittany Murphy did dark to break out of her dizzy blonde romantic comedy persona. It didn't work. Now she's back to blonde and starring in the upcoming thriller, "The Dead Girl."

Sarah Jessica Parker let her hair go brown when "Sex and the City" ended. But she's drifted back to lighter locks for the romantic comedy "Failure to Launch" and her upcoming roles in "Spinning Into Butter" and "Slammer."

But going dark is working for Lindsay Lohan. The child star wanted to carve out an adult acting career after teen queen roles in movies like "Mean Girls," " Freaky Friday" and "Confessions of a Teenage Drama Queen."

With her long dark hair, she's receiving good reviews for her role in "Bobby," the Weinstein Company's Oscar 2007 bait and her work in the upcoming "Georgia Rule" with Jane Fonda.

And check out these impressive non-blonde bimbo roles. Lohan's set to star in "A Woman of No Importance," based on an Oscar Wilde play. She'll play Welsh poet Dylan Thomas' wife Caitlin in "The Best Time of Our Lives." And she's appearing in "Speechless," a modern-day Cyrano tale.

Cameron Diaz went dark for her BAFTA-nominated role in the quirky "Being John Malkovich" and did deep auburn for her Golden Globe-nominated role in Martin Scorsese's "Gangs of New York."

But she was raced back to being a dumb blonde for "Charlie's Angels: Full Throttle" and "In Her Shoes."

As far as Britney is concerned, some say she did it to look more like a serious (and capable) mom. Good luck with that. Others say she did the dye job just for her Vanity Fair cover. Either way, the hair color scheme backfired and she was criticized for using hair dye while pregnant, a widely accepted no-no.

Negin Zand, the top colorist at Sally Hershberger's star-studded salon on Melrose Place, has taken quite a few of her clients - Kim Bassinger, Evan Rachel Wood, Rachel Mcadams, Kate Bosworth, Cate Blanchett, Scarlett Johansson and Paris Hilton - from light to dark and back again.

"The way to make blondes look good as brunettes is to make it look real," Zand advises. "It should always look soft and natural, not goth or inky."

She advises making the hairline a little lighter than the rest of the hair. "The hair that frames the face should never look too dark or your face will look too hard. I also do a little bit of tipping because natural hair is never just one color. Your hair should have enough dimension that it never looks flat."

For shine and to extend the color, she uses the new John Frieda color glaze and a dab of John Frieda Frizz Ease hair serum.

And when you're ready to go back to your blonde roots, she'll take you there safely.