For the Ladies:
Hats go with the Derby like mint goes with the julep! Large brimmed, feminine, and frilly are most popular, but be creative. You can include fabric, tulle, fake flowers, real flowers, feathers, and more on your hats. And of course, design the rest of your outfit around the hat. Sundresses, skirts, and Sunday attire usually best fits the bill.
For the Gents:
Business casual is typical, blazers, jackets, ties etc. (for the party, you don't have to get that fancied up if you don't want to, but feel free to if you are feeling froggy!) Seersucker, suspenders, bow ties, and ties are always a hit too. Polos and shorts are acceptable depending on where you are sitting. Dress to accommodate your lady friend!
Pictures courtesy of here
Disclaimer:
If you are planning to attend the Harville Kentucky Derby Party, please do not feel like you MUST dress up. Of course it is encouraged, and adds to the fun, but is not mandatory! These are just some fun ideas and an excuse to dress for the occasion if you feel so inclined! Hope to see you there!!