Matching Black & White
While we call black and white colors in their own right, they are actually not.
Technically speaking, white is the complete absence of color combined with a maximum of lightness. Black, on the other hand, is a combination of all colors with a maximum level of darkness.
Both white and black can be combined with any color (even themselves) and work well. These "colors" are considered exceptions to the rules of color matching.
See also: Color matching