Save Behavior Properties

I am creating a web page where the user can select what color they want the
background to be. When it first loads, the background is white and I have the
bahvior set to change the background color to another one. I want the the color
the user chooses to be the one that they always see when they visit the site
again (granted it could be changed my them again if desired). How do I do this?
Cookies i was guessing? I dont know. Any help would be great! Thanks