Quote jonny the leyther="jonny the leyther"Forgive my ignorance, what's a full blue and a half blue? I didn't go to uni!'"
A blue, in the case of these Unis is generally awarded for being picked to represent the combined colleges of that University in a sporting or sometimes academic competition.
A half Blue is just a way of trying to keep the actual "blue' from being diluted.....otherwise they would be handing them out for knitting, Ironing and getting the most posts on a chatroom thread
In other countries, it can be awarded to a student who proved themselves the best at a particular dicipline, sporting or otherwise over the year across the whole country and generally at High School Leaving age.