The major dysfunction is with red/green and yellow in majority of colour blind people.....I guess the DL will have special medical notes. Maybe a stricter policy is in place for very rare case of total col blindness wherein only Black and white is visible....although I believe, B/W col blind people can differentiate between the hues and gradation/intensity/shades of colours. Also as the pattern of lights that appears is same world wide which is red, yellow and then green....people self teach or are advised accordingly.
