So I just happened to be caught in a conversation between two dog lovers during which a dog with two different eye colours was brought up. I say "that happens in humans as well". The reaction is "get out of here", that's not possible. Essentially that it is absurd.
So recalling it now I did some checking and surprise surprise, its called "Complete Heterochromia". Plain Heterochromia involves slight variations in eye colour.
Now I shall treat myself a proverbial cookie because I'm an arrogant SOB!