Light Detection
Every object reflects light. The human eye is only able to pick up on a small range of this light, called the visible spectrum. Some insects only see the infrared spectrum. There are tools to make other forms of light visible, but without aid, the eye can only see the colors of the rainbow. Inherited disorders of the eye causes people to confuse one color for another -- a condition commonly called color blindness. It is very rare for someone to be completely color blind. The most common type of color blindness is the inability to distinguish red from green.