I know very little about color blindness. Are you familiar with this disorder?
Yes, it is a deficiency where a person has decreased ability to see differences in color.
Can they see any colors at all or is everything black and white?
They just see more dull colors. Complete color blindness can also cause decreased visual activity.
Are those impaired allowed to obtain a driver's license?
Yes. They have a decreased ability to recognize colors but they would still understand the signs with whatever color they see.