We are investigating the cause of this, and will be attempting to make it work with all websites. Currently, we can only get it to pull colors from a few websites, like www.knowledgeowl.com (our help docs site) and a few other websites we have randomly tried. We will keep you updated here!
This issue has been addressed. Right now this feature will only look at the first 3 CSS files on a webpage. Any colors in a file past those first 3 will not be found.