To LIPS I think it is a case of whether or not the guy knew he had a colour vision problem which would have made him ineligible for a GCAA licence. If he did know and had managed to cheat his way through the tests for a number of years (not a difficult thing to do) then it would be a pre-existing condition which he had not disclosed. No insurance company would pay up under those circumstances regardless of what Emirates or the GCAA had done.
I'm not a opthamologist (heck, I can barely spell it!) but I've never heard of somebody "becoming" colour blind. I always thought you were either born with it or you weren't.