Meet Hugh. Hugh allows anyone on the web to change the colors of your site. Permanently... At least until the next person comes along and changes your site's colors.
After you install the plugin and activate it, simply add the Hugh color widget to one of your widget areas.
Hugh is not a plugin you should use if you're interested in customizing the colors of your site. Hugh is a plugin you should use if you're interested in letting everyone customize the colors of your site.