Colour blindness afflicts about 1 in 12 men in the world. Women are far less affected because they have two X chromosomes. Men only have one X chromosome and therefore there is no backup if the gene for good colour vision is damaged or changed. Of course, colour blindness is a misnomer. Very few people indeed are really colour blind and the term colour defective is scientifically more correct. So-called colour blind people have trouble discriminating between colours that the rest of us see as different. Most commonly the difficult is in telling reds and greens apart which is where the term red-green colour blind derives from. Though people need to be able to pass colour-vision test before they can be employed in certain professions (such as being an aeroplane pilot) where colour decisions are critical, everyone is allowed to drive a car. Even though traffic lights are red and green!!
The argument for allowing colour blind people to drive has always been, I think, that drivers quickly learn the positions of lights. Red, is on top, amber in the middle and green on the bottom. However, is that red-amber-green order used everywhere in the world. It is used in the UK where I live. But elsewhere?
Whether to do with the order of the lights or not, several studies have shown that colour blindness is a risk factor in driving. Hence the development of the UniSignal (Universal Signal Light). Developed in South Korea the UniSignal uses different shapes for different colours so that drivers can recognise which light is on whatever the order in the particular city in which they find themselves.
Kandinsky would approve!