The Queen is being backed to wear a blue hat at the royal wedding.
In the run up to Prince Harry and Meghan Markle's high profile ceremony, bookmakers Ladbrokes has set blue as the favourite at 2/1, followed by pink at 3/1.
The Queen, who is Harry's grandmother, is known for her signature bright block colours and matching hats.
Punters are being given odds of 7/2 that the monarch will opt for purple, and 4/1 that she picks yellow - the same colour she wore to the Duke and Duchess of Cambridge's wedding.
A shade of cream or ivory - traditionally the reserve of the bride - is 6/1, while orange is 8/1 and gold 12/1.
Jessica Bridge of Ladbrokes said: "It might be Meghan's big day, but Her Majesty rules the roost and attention is now turning to her outfit of choice."
She added: "Punters think she'll be wearing a shade of blue at Harry's wedding.
"However, purple is also proving to be a popular bet at 7/2."
For the Trooping the Colour parade marking her official 90th birthday, the Queen wore a vivid flourescent green.
Ladbrokes has green at odds of 5/1.