Mario es daltónico y por eso no ve el color de los semáforos como los demás.Mario is colour-blind and that's why he cannot see the colour of traffic lights like everybody else.
This means that the noun can be masculine or feminine, depending on the gender of person it refers to (e.g. el doctor, la doctora).
No conozco a un solo daltónico, pero sé que no pueden distinguir ciertos colores.I don't know a single color-blind person but I do know that they can't tell the difference between certain colors.