A Green Endorsement is awarded for an "instance of exceptional flying skill and judgement" or something like that. You get it for doing something good in the air that doesn't quite rate a medal. You get 2 copies of the narrative (a bit like a mention in dispatches I suppose) and they are signed by the AOC. One you are supposed to stick in your log book (it is a Green Endorsement to your Flying Log Book) and the other you frame and hang up in your toilet next to pictures of members of the Royal Family you have met.
A Red Endorsement is, I believe, still possible to be awarded although it has been a long time since it happened. It's like a Green Endorsement, only it's for something bad that doesn't quite rate a jail sentence and usually follows an inspection of the AOC's office while wearing your best blues!
The only other colourful addition to your log book is combat time which should be recorded in green ink.