@duerer it is all about masking; if you have a bunch of Irish people on St. Patrick’s Day, a Green Screen might not be the best idea ;)e
As far as I know, Blue Screens were common ‘in the old days’ and for some reason they mainly switched to Green.
I really need to re-watch: https://cgcookie.com/course/introduction-to-compositing-in-blender
And this might also be helpful: https://cgcookie.com/course/green-screen-compositing
