The 2015 guidelines on dress code, detailed in full on the Royal Ascot website, are pretty prescriptive, especially for racegoers in the higher echelons of the Royal Enclosure.
The festival is always well attended but organisers are taking no chances this year with a giant screen being erected to broadcast the FA Cup Final to racegoers.
Among the cheering crowds were many racegoers who embraced the Diamond Jubilee theme, with variations on the red, white and blue color scheme visibly in evidence among the usual confection of hats and headpieces.