I'm working on a very new site installation. Clean installation of WordPress 3.9. No plugins installed; all native plugins not activated. When I activate and go to "Customize" under the Twenty Thirteen theme, the "Colors" section doesn't load. I've tried this on several different computers/OS's and still the same thing. Where can I start to troubleshoot this? I don't want to have to go in and hand-edit the CSS. Thank you!