Sometimes a person without experience or training is referred to as being "green".
They can be referred to as being green.
color blindnesss
If a person is without color vision, there is really no way to regain it. There are types of lenses that can improve some color loss, but it cannot be regained.
Well, first you have to get accepted into Hogwarts. Then you have to have experience of color-changing spells, which are much more complicated when performed on yourself. Or you could get some color contacts....But whatever.
hue
The color is a redish-brown (I know from experience!).
Green. A green pony can be any color; it simply means the pony is young and needs training to develop its skills. In other words, the pony is 'green'.
In order to experience color constancy it is helpful to view its relation to surrounding objects.
Black
No, because a person is a human, not a color.
The term for picking on someone based on their race or ethnicity is racial discrimination or racism. It is important to promote equality and respect for all individuals regardless of their race or ethnicity.
If the person has been blind all of their life, explaining color to them would be impossible. How can anyone have a conception of what color even means, if they never had the experience of seeing anything except darkness