She broke out the green and gold back in 2008, but for her arrival on the Australian runway Kate has gone for gold.
Wearing a sunny yellow dress by Roksanda Ilinčić, a London-based Serbian fashion designer, the Duchess made a nod to our official colours.
Classic with a twist, in this case of lemon, seems to be Catherine's fashion theme du jour for the royal tour thus far.
Catherine was the star attraction at the Opera House on Wednesday.
And if the New Zealand leg of the tour is anything to go by, there won't be a whole lot of leg on show here either.
"I'd love to see her in a Zimmerman bikini on Bondi Beach," says former fashion editor for Fairfax, Paula Joye.
There is a trip to Sydney's Manly beach on the royal itinerary but, with the world watching, the chances of Kate whipping off her kit Joye admits, "are zero".
Prince William, Catherine and Prince George disembark at Sydney airport on April 16, 2014. Photo: WILLIAM WEST
Rather, we can expect respectable hemlines and a noble nod or two to local designers.
"She has a definite style now," Joye says. "Her staples are cap-sleeve or to-the-knee dresses, usually waisted or with a slight flare; coat dresses; skinny jeans and a blazer or a ballgown...
"In terms of the designers we have that would suit her style and taste, I think she would like Tony Maticevski and... Josh Goot. I'd love to see her in something really Australian though - Sass & Bide, a Zimmerman cocktail dress or Ellery."
Kate Middleton wears green and gold in 2008. Photo: Antony Jones
Kate may also don Collette Dinnigan, whose dresses she has worn before and possibly even Aurelio Costarella who designed the stunning silver coat that former PM Julia Gillard wore to the royal wedding in 2011.
Whoever she chooses wear, we can expect a splash of colour.
"Her pallette is navy, red, white and a touch of jade green or sea-foam blue," says Joye. "They are all regal colours - the colours of the Union Jack."
Duchess of Cambridge wearing a Collette Dinnigan dress. Photo: Ikon Pictures
She accessorises with minimal makeup, her hair either down or pulled back into a ponytail and always a smile.
Prim and proper she may be but Catherine is definitely not dull. Warm and unafraid of colour, the Duchess also likes a serious stiletto.
Whilst in New Zealand she managed to play cricket in three-inch high heels.
Catherine, who is reportedly travelling with the Queen's stylist as well as a hair stylist and a stash of the Queen's jewels, also seamlessly mixed designer threads with high street brands.
She favoured designs by the late Catherine Walker, who often dressed Diana, and Alexander McQueen, whose design she wore to the Queen's Diamond Jubilee. Keeping it real, she also recycled outfits and dressed down in mainstream labels like Zara and J Brand.
Thrice, on tour of New Zealand, she wore designs by Kiwis.
Along with a diamond and platinum silver fern brooch, that was a Christmas gift to the Queen from the Women of Auckland during the Commonwealth Tour of 1953-4, Catherine wore outfits by London-based designer Emilia Wickstead and New York-based designer Rebecca Taylor.
For Catherine, William and George's 10 days in Australia, starting today, there are strict dress requirements, which the 200-odd contingent of reporters following the royal tour also have to abide by.
For the most part, these include instructions to wear "casual, closed-toe shoes", "smart casual" or "business suit/day dress".
Despite several reception dinners, at no point is there the opportunity - for royals or reporters alike - to pull out the tiaras.
It would be fun to see her rock out the royal rocks, but the Duchess manages to look immaculate and impress no matter what she is wearing.
"I think she's smart and she likes fashion," says Joye. "Also, she is our Queen to be and I think she will try to win over her subjects one dress at a time."