Running multiple tests on buttons right now - and I've read/been given advice that a) orange is good and b) you want the color of your button to be different than the general colors on your sight to draw attention to it.

I think language matters equally as much - especially if you have primary and secondary text in the button - but these are all hunches, hence the testing. Found a ~80% uplift with 99% confidence just by flipping the primary and secondary text of a button on our homepage (not our primary landing pages) last week. Testing color variations on the improved text now.

source: http://www.formstack.com/the-anatomy-of-a-perfect-landing-pa... (note I don't agree with all of this but there is a good color breakdown). also had some real world advice given to me from a convo with a 500 startups founder a few months back related to orange.