How Kate is using the Queen's key trick to increase her 'visibility'

Kate also wore head-to-toe purple for the inaugural Shaping Us National Symposium, where she opted for an Emilia Wickstead trouser suit.

According to Sarah Vine, who occasionally comments on the Royal Family, this was a tactic first used by Queen Elizabeth II.

WATCH NOW: Princess Kate greets the President of South Korea

She said: "This was a classic tactic that the Queen had.

"She knew she was quite a small person in a sea of people, so the best way to get noticed was to just wear the same colour from top to toe.

"You were either an orange person or a purple person or a green person and everyone can see you.

"She was very visible and now Catherine has done that."

Referring to Kate's Emilia Wickstead suit, Vine also told Palace Confidential: "It was Quality Street purple, that's what I'd call it."

The princess paired her purple suit with Gianvito Rossi 105 Pumps in Navy Suede.

In addition, she opted for Princess Diana's Cabochon Sapphire Drop Earrings.

For Tuesday's outing when Kate greeted the President and First Lady of South Korea, she wore a stunning Catherine Walker "Beau Tie" coat-dress in scarlet red.

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She paired the number with a wide-brim felt hat in the same colour by Jane Taylor.

The 41-year-old also carried her Miu Miu bow-embellished red suede bag.

For footwear, Kate wore red Gianvito Rossi 105 suede pumps.

The mother-of-three completed the elegant ensemble with Princess Diana's Cabochon Sapphire Drop Earrings.