Sartorial diplomacy is nothing new for Princess Kate , and she honored Oman with a green outfit as the Royal Family welcomed Sultan Haitham bin Tarik for a state visit at Windsor Castle on October 20.

Oman’s flag features shades of green, white and red, and although the country’s green is a much brighter color, the Princess of Wales wore an old favorite Sarah Burton for Alexander McQueen coat in a rich forest hue Tuesday.

Burton, who designed Kate’s wedding dress , is now creative director at Givenchy, and the Princess of Wales continues to wear her old McQueen pieces such as her fitted coat with flap pockets.

The Princess of Wales curtsies to Sultan Haitham bin Tarik at the start of his state visit to Britain.

(Image credit: Getty Images)

Kate wears a pair of Cassandra Goad earrings and a Juliette Botterill hat.

(Image credit: Getty Images)

Underneath, the Princess of Wales wore a lace turtleneck dress or top, but once inside the castle, she swapped it for a simple dark green turtleneck dress by…