Depending on whom you talk to, people will generally argue that either green or red is the end-all-be-all color to drive conversions, but there hasn't actually been concrete evidence that any specific color performs better than another. The reason for this is simple: there are all sorts of different people in the world with all sorts of different preferences.
Fortunately, there are a few guidelines to follow that will help you pick the right colors for your CTAs. Below are three ways to find out what your specific client-base responds best to.