Black is the absence of color. And here's why:
Light is white, and white is the combination of all colors in the visible spectrum. They are Red, Orange, Yellow, Green, Blue, Indigo and Violet (ROYGBIV).
In light, a white object reflects all of these colors equally. A blue object reflects primarily blue and absorbs all other colors.
Where there is no light, there is no color. So there is blackness.
Hope that helps.