The color is being saved in a cookie set via javascript.
This is more of a JavaScript question.
How to change the background color with a color picker: http://stackoverflow.com/questions/4146621/changing-colors-with-jquery-with-a-color-pickerhttps://stackoverflow.com/questions/4146621/changing-colors-with-jquery-with-a-color-picker
How to use jQuery to manage cookies: http://www.ilovecolors.com.ar/using-cookies-jquery/
