1 How come when you wear a black shirt in the sun it becomes warm, while a white shirt does not?
The color black absorbs light, while the color white reflects it- Eric
to expand on Eric's explanation we must recognize black and white in terms of light as opposed to pigments in the context of the black shirt/white shirt question. Black absorbs light because it is the absense of any color being reflected, all light is being absorbed. While white is the combination of all colors so nothing is being absorbed to create heat.

Thanks Daina, this was very informative, and will help me with my color corection when i edit movies. --Eric why can you never seem to spell my name correctly?

2 If the sum of all colors is white, why is it that mixing red, yellow and blue result in gray? -Robert Townley This is a matter of the difference between pigments and light. White light is produced only when all the colors of visible light on the spectrum are combined. But when pigments, such as oil paints are mixed up the result is a gray or brown color because when a primary pigment is mixed with a secondary pigment, the result is black.

3 So if people are color blind, does that mean they are unable to view certain parts of the light spectrum? Rafi. color blindness is more of a cerebral disability rather than a deficiency connected to the viewer's eyeballs. Color blindess has to do with a lack of cone cells in the retina that allow people to perceive color. Color blind people's ability to discern color has to do more with the absorbtion level of the cones than the actual color spectrum