But which colour is most popular?
According to recent Pinterest data, fans are most drawn to her red looks. The queen's scarlet, ruby and vermilion outfits are the most frequently pinned, and have been shared nearly 10,000 times.
Scroll through the gallery above to see a chronology of the queen in red, with outfits dating back throughout her reign.
The sartorial choice of vibrant red is no accident. The queen has worn cherry hues to attend Canada Day celebrations in Ottawa and mirrored the Qatari flag by wearing a carmine coat to welcome country's Emir to Windsor Castle in 2010. It is also a festive favourite, often chosen for walks to attend the Christmas Day church service.
Significantly, red also the national colour of both England and Wales, and one of the three British national colours, alongside white and blue. It is the colour of roses, England's national flower, and a shade synonymous with London, thanks to the city's vibrant red double-decker buses, traditional telephone boxes and pillar-box red post boxes — although the latter two are found across the UK.
There are also military associations with the colour red. The red coat, or scarlet tunic, has been used by the British Army since the 17th century; and it is a powerful colour, associated with pride, confidence and courage.
When the queen steps out for official engagements, there is an element of dressing for a service job, says British historian Robert Lacey.
Lacey explained why she frequently chooses to wear hats, saying: "Very few modern women wear a hat as part of their work uniform, aside from perhaps members of the armed forces ... It's a reminder that the queen is indentured to a service, to a job."
There is also a practical reason why the monarch always chooses vibrant colours and matching hats for engagements — they ensure members of the public can spot her in a crowd says her daughter-in-law, Sophie, Countess of Wessex.
“She needs to stand out for people to be able to say, ‘I saw the queen’,” the countess said in the 2016 documentary The Queen at 90.
“Don’t forget that when she turns up somewhere, the crowds are two, three, four, 10, 15 deep, and someone wants to be able to say they saw a bit of the queen’s hat as she went past.”