At the risk of coming over all Alan Partridge, it's there in yellow, blue and black on pages eight and nine of the 81-page booklet dealing with Law 12 (fouls and misconduct). That's Fifa's colour coding not mine. There is a colour missing, though, and that is grey.
Was Nani careless, reckless or using excessive force? Careless and it's a free-kick, reckless add a yellow card. Red is appropriate if "the player has far exceeded the necessary use of force and is in danger of injuring an opponent".
Nani's challenge could clearly have injured his opponent but did he exceed the necessary use of force? It's more than possible for Cuneyt Cakir to make that case amid the hurly-burly of the contest on seeing, at first glance (which is the only glance a referee gets) Nani's boot in Alvaro Arbeloa's chest. Former referee Dermot Gallagher pointed out that a referee can only follow the guidelines laid out for him and, according to those, Cakir is not wrong and Roy Keane's lonely stance in saying the referee got it right is right. But then Gallagher said he would not have dismissed Nani; he would have interpreted the guidelines differently. Different referees from different footballing cultures will come to different conclusions. There are always shades of grey.