Do you have your own Colorpicker which is saving the value in a cookie?
If yes=>
PHP:
XenForo_Helper_Cookie::getCookie('SkinColor')
If it's not working, check the cookie names!
XenForo adds automatic a "cookie prefix" to the name, maybe you'll need to rewrite the colorpicker code OR write your own method to read the cookie
I am using http://www.eyecon.ro/colorpicker/ , same thing I use on my IPB skins that are in development except this one is jQuery and not Prototype.
Also as I don't know anything about php or stuff like that instead of how to edit it to my needs, how would I go about putting that in a template and/or working it like the code I supplied in the OP?