You need to pass a color-blindness test to get a driving license in my home country and I can't tell you how much I struggled with it 15 years ago. The reason is exactly this -- I can work out traffic lights very easily although I'm r/g colorblind, however the test was about showing a number of different colors and asking you to name them. I failed, obviously, but the instructor did a favor and marked me as passed.
I still have no idea what practicality that test provides in driving.
As a kid I always wanted to be a pilot, but to get a license you can't be colour-blind. I guess because light colours on runways and such confer meaning, or something like that.
I had no idea there were countries demanding this for a driving test though - I mean, it's not like they randomise the order of traffic lights!
I still have no idea what practicality that test provides in driving.