As you can guess from the lack of response: this is not really possible. CSS is not meant to be dynamic. You could define a few CSS-classes though with several colors and let the user pick one of those. You can set the color dynamically with javascript, so that is an option. Lastly, if you want the user to select Cooperation colors or something else that does not change a lot, you can consider creating a CSS file with that color and include it in the index.html. That should work as well, although caching will be an issue.