"It wasn't just the men either - women looked at me too."
McCarthy isn't the only high-profile woman to make the switch from brunette to blonde, although most don't do it as an unscientific stunt for their newspaper.
Others to make the dramatic change include Hollywood stars Scarlett Johansson, Cameron Diaz and Katherine Heigl.
New Zealand's Anna Paquin has also noticed the powerful effect of lighter tresses.
"People stare at blonde people more than they stare at brunettes. I guess it's because it's bright and shiny and it catches the light," she told New Zealand Woman's Weekly.
So do we prefer women with hair of a lighter hue? Are we born or conditioned to be drawn to them? And are they treated differently?
Daily Mail columnist Samantha Brick sparked reaction around the world - much of it critical - when she wrote about how many men lusted after her because "I'm tall, slim, blonde and, so I'm often told, a good-looking woman".
Strange men fell over themselves to pay her taxi fare, buy her drinks, give her flowers and even treat her to champagne because of her "pleasing appearance", she said.
There's been plenty of research about why, one study concluding that cavemen, rather than gentlemen, initially preferred blondes.
Canadian author Peter Frost found northern European women with light hair and blue eyes at the end of the Ice Age attracted men because they stood out from the more common brunettes.
He suggests blonde hair evolved from a genetic mutation when there was a shortage of food and men meaning "women had to compete for a limited supply of potential husbands".
Other research suggests blonde hair on women can signal youth and therefore fertility.
That fits with this week's revelation that the organiser of Miss Universe New Zealand asked judges to crown a blonde to please a sponsor.
Three judges told how they fell out with director Val Lott last year after ignoring pressure to put a blonde contestant on the podium.
But psychologist Sara Chatwin does not believe there is any innate attraction to blondes and says preferences for certain physical features are learned.
From the moment we're born, we're bombarded with images of fairytale princesses with long blonde locks," she says.
We graduate to images of perfection in adverts and celebrity culture that condition us to find certain features desirable.
So it's no coincidence that facial symmetry, flawless skin, slimness, big eyes, and for many, blonde hair are considered attractive in much of Western world.
"It's sensationalism and buying into that notion that blondes have more fun," says Chatwin.
Some TV viewers agree. Twenty-seven-year-old blonde Chelsea Winter's victory in this week's MasterChef final prompted all kinds of internet-based conspiracy theories.
Paul Kamau summed them up on the Herald's Facebook page, writing: "She fits the stereotype and will look good on the cover of women's magazines. So it's a win-win for everyone. God please give us some decent drama on TV not this kind of crap."
MasterChef judge Simon Gault dismissed the notion Winter won for anything but talent as "ridiculous".
"She's outstanding - you win the challenges and you win."
Chatwin says media shapes our perceptions.
"There are a lot of blondes on our TV screens - Ginette's on Good Morning, you've got Pippa who used to be on with Paul, Wendy reading the news, she's blonde."
But it was attractiveness rather than blondness that turned heads.
The change from brunette to blonde often follows a relationship break-up, marriage or childbirth, say hairdressers.
Wellington hairdresser Tania says some customers even get their hair dyed to please partners who prefer blondes. The time and money spent maintaining their hair is worth it, say the bottle blondes.
Mimi Kelly, 38, has been colouring her hair for much of her adult life, and has no doubt it makes people respond to her differently.
"If you're waiting and you need a break in the traffic, some guy's going to stop and let you go - he can't see your face but he can see your blonde hair and for some reason that catches their eye. I find people are nice to you when you're blonde and when you're darker I've found that I don't get that same attention."
The Aucklander says 70 per cent of her clients are blondes.
Many return to the colour after experiencing life as a brunette.
"I've had a lot of clients who have gone darker, even just a couple of shades darker, and they have felt they haven't got the same attention and they're like, 'I need to go back'."
Although blondes get more attention, it's not always the right kind.
Mrs Kelly says hitting the peroxide can have its down side. Some people become "blondorexic" - obsessed with being blonde.
"They can't get blonde enough and you've got to pull them back a bit and say 'you're going to look like the girls of the Playboy Mansion if you go down that road'."
Then there's being the butt of jokes that stereotype you as stupid or promiscuous because of your hair colour and, as Samantha Brick details, jealousy from other women.
Even worse, being blonde might be a bar to lifelong happiness.
Men often see blondes as fun, but overwhelmingly want brunettes as long-term partners, says Sasha Madarasz, director of Two's Company, an organisation offering one-to-one introductions to singles.
Of the men who talked about their preferred hair colour in a partner, about 90 per cent want a brunette, she says.
"My male clients are looking for a serious relationship and I think for the long term they prefer brunettes."
The final word goes to McCarthy. At the end of her week, she was thrilled to go back to the anonymity of her dark hair.
"It may be societal, mythical, biological or sexual, but blondes have an immediate effect," she wrote. "It's not for everyone of course."
- with Hana Garrett-Walker (brunette)
