Here’s a good article titled Which Color Converts Best? The title is slightly misleading as it really emphasises the role of colour in visual hierarchy in relation to the design of the rest of the page. Something I think designers often miss when trying to figure out what colours convert best.

Color usage does matter, sometimes a lot. But saying that one color converts better than another is simply stupid. There is no universal best color. What works on one site, doesn’t necessarily work on another.

Visual hierarchy matters and making your call to actions stand out matters. So “green vs red” is not so much about the color, but “does the important stuff stand out enough” and if not, how can we improve the situation.