Color Blindness

As I was processing my medical exam as a requirement for my non-professional driver's license, I was shown plates of dots with different colors and was asked of the number shown within the circle. At first I promptly answered the doctor with the number I see but as he switched to the next plate, I wondered why he's asking for a number but I can't see any. It's the same for the next plates up to the last. This plates, as  I learned later, were color plates in Ishihara Test used in diagnosing color blindness. It was then that I was officially diagnosed as a Color Blind person. 

After I went home, I got curious about color blindness and here's what I've learned.
 
Color Blindness
Color blindness is the inability to see certain colors in the usual way.