The long-established fashion was started with Col. Meriwether Lewis Clark Jr.'s vision for the Derby as an event that the high-class would attend, similar to European-style racing events, which mandated full morning dress for men and women. For the first running of the Kentucky Derby, he used high-class women to recruit his target clientele to attend the race. The event quickly became just as much about the fashion as the racing. Going to a horse racing event became an opportunity to show off the latest in spring fashion and women were known to coordinate their hats, dresses, bags, shoes, and even parasols.
The extravagant hats that have become associated with the Kentucky Derby did not really come around until the 1960s, when social fashion norms loosened up and the presence of television gave women a reason to stand out. The hats became larger, brighter, and more extravagant.
Hats at the Kentucky Derby have become even more popular after the royal wedding in 2011, an event that showcased many elaborate hats and fascinators.
Whatever you celebrate--may it be a super great day!