This is amazing: a change in the color of the CTA had dramatic impact on the results! Goes to show that it's almost always about blocking and tackling (to our non U.S. readers, that's an American Football reference to talks to the basics).  Moral of the story: always test the basics first...

We tested three versions of the identical call-to-action. The messaging was exactly the same, but we varied the color. One was a black background that highly contrasted the page and the other were almost identical – just varying the button color.  The results are interesting – the CTA with the green button outperforms the other CTAs by almost double! The green button version resulted in less clicks, but a much higher conversion rate.