This is probably a stupid question, but how do I revert/undo a change that I made to a Theme?

For example, I opened the Preferences menu, then went to "Fonts and Colors", and messed around with shading, etc.

I clicked on "Selection", because I wanted to darken the color of selected text. However, I did something to mess it up. There's no "Cancel" button or "Undo" menu item, so what do I do if I don't want to save my changes to the colors?

I suspect that the best idea would be to copy the color theme before editing, but that seems sort of kludgy.

Thanks, --Nate