What makes a good CTA?
A good CTA promotes a high value yet is low risk for your audience. Employ a zero-pressure approach. Let your audience know that they are simply finding out more without committing to anything.
Which CTA works best?
Generally speaking, green and orange buttons are reported to perform best. Ultimately though it will depend on your site design, as contrasting colors work best to make striking buttons that stand out. You wouldn't want a green CTA button on a green background.