I just read this article which discusses whether red or green is a more intuitive button colour for a call to action.
What do you reckon?
I like to distance myself from red for actions, unless it is performing a specific delete/cancel/undo type action - where the user will either do something that they may regret later, or to take them out of a flow that they are already in. That’s just a personal preference though - I know a lot of big brands use it to reinforce the urgency needed to take an action - “Get it before it’s too late!” would be less urgent if it was on green, rather than red.
Also I think it depends a little on the site wide colours, and also the specific action you are taking. A blue search button looks way more natural to me than a green (or red) would (Google and eBay wouldn’t look right with another colour). A “Register” button on the other hand less so.
It´s clearly green because people will be afraid to push the red button. Red may be easier to see in terms of visibility but red as is strongly connected with danger … has a lower call to action.
Green on the other side is stronger than other colours because it communicates … everything ok.
Anyway you shouldn´t base a decision on simply colour as meaning can change extremely based on experience and context.
Dean is giving a nice example where it happens.
Taking the question further you could even discuss multiple colours, integration of icons or visual Effects.
There may even be pages where rainbow colours get the strongest call to action 
I wonder whether it depends on the size of the commitment the CTA is demanding—whether it’s a big commitment (e.g. buy something) or a small one (e.g. vote in this poll).
I haven’t read the article, but I imagine there are so many other factors (brand palette, audience, cultural) that having a definitive guide for colour feels like asking “which is tastier, lemon or coffee gelati?”
I think contrast matters more than color alone. You want your CTA to be highly visible. Say you have a background over which a green CTA has low contrast… that makes for a poor choice.
This is one of those “it depends” things (isn’t that all UX?). Relationship to other items via size, spacing, contrast. I suppose if you’re using red as a color for warning messages, it’s good to stay away from.