If you view their 'scripts.js' file, they generate a random color palette(jQuery) when users come to the page. The full palette is: orange, amber, indigo, turquoise, navy, teal, and lime. There may be more. You'd have to look at their colors.css file.
I guess they're A/B testing their colors? I'm getting a nicer teal while my coworkers are getting a brighter green. Anybody else seeing this?