allowing the user to use custom themes by storing them on their browser, or locally or something. Not sure the best way to do that.
A new UI that allows the user to change the colors of the websites theme. Could possibly do this by generating a CSS file after user is done editing, then loading that in on the page dynamically, or just inserting the style tags directly into the header.
would also need color select tools which I'm entirely unfamiliar with.
Custom themes
This would entail two pieces: