The royal family often writes letters to charities, their patronages and individuals and fans have noticed a difference on the notepaper used by the Queen, the Prince of Wales, the Duke and Duchess of Cambridge, and the Duke and Duchess of Sussex.
Each royal has his or her own monogram, usually with their individual initial and a crown logo, known as a coronet above it, and fans have noticed that each family member uses a different colour.
Typically, the Queen, Prince Charles and Prince William all use a red monogram on their stationery, as noted by Gert's Royals on Twitter.
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Despite stepping back as senior royals last year, the Duke and Duchess of Sussex had continued to use headed notepaper with their blue monograms, consisting of an intertwined 'H' and 'M' with their coronet.
The reason behind this appeared to be because Harry is the son of an heir apparent.
Earlier this week, Prince Harry and Meghan unveiled their brand new stationery with their Archewell logo earlier this week, as an East London school shared a letter from the Duchess on Twitter.
Harry and Meghan's joint monogram
When Prince William and Prince Harry set up their own royal household in 2009, they revealed their own individual royal cyphers, with Harry choosing a similar blue colour to that of his late mother Diana, Princess of Wales.
Meanwhile, the Duchess of Cambridge typically uses a gold monogram on her headed notepaper.
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Kate uses a gold monogram
The reason behind the different colours has never been confirmed by the palace and it's not just the senior working royals who have distinct monograms.
Princess Beatrice has been known to use a bee symbol with her coronet above it – in a nod to her family nickname.
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