So as @didrocks points out, the actual name in Gnome is “suggested action”:
@meetdilip, in my explanation I only mention “destructive” for red buttons. Green should be the action that the app developer or the OS developer suggests you click on in 99% of the cases. This gives the user an additional confirmation that what he is doing is “correct”. It’s ok to press the green button since that will “do the right thing” in 99% of the cases. For the login screen, 99% of the cases, a user wants to login.
@didrocks, is there any notion of a “destructive” action in Gnome? Either “an action you should not do” of “a dangerous action”?