There are multiple types of color blindness, but the most common types involve an inability to distinguish between either red and green or blue and yellow. This causes problems seeing other colors, because a color blind person cannot see elements of the color he is blind to within other colors.
On average, a color blind person can only identify five out of 24 colored pencils correctly. Color blindness can be an inherited trait, or it can be something that happens as a result of illness or aging. As of 1999, approximately 8 percent of males and 0.5 percent of females had a form of color blindness. Partial color blindness is much more common than total color blindness.