colour

A Closer Look

When beams of colored light are mixed, or added, their wavelengths combine to form other colors. All spectral colors can be formed by mixing wavelengths corresponding to the additive primaries red, green, and blue. When two of the additive primaries are mixed in equal proportion, they form the complement of the third. Thus cyan (a mixture of green and blue) is the complement of red; magenta (a mixture of blue and red) is the complement of green; and yellow (a mixture of red and green) is the complement of blue. Mixing the three additive primaries in equal proportions reconstitutes white light. When light passes through a color filter, certain wavelengths are absorbed, or subtracted, while others are transmitted. The subtractive primaries cyan, magenta, and yellow can be combined using overlapping filters to form all other colors. When two of the subtractive primaries are combined in equal proportion, they form the additive primary whose wavelength they share. Thus overlapping filters of cyan (blue and green) and magenta (blue and red) filter out all wavelengths except blue; magenta (blue and red) and yellow (red and green) transmit only red; and yellow (red and green) and cyan (blue and green) transmit only green. Combining all three subtractive primaries in equal proportions filters out all wavelengths, producing black. Light striking a colored surface behaves similarly to light passing through a filter, with certain wavelengths being absorbed and others reflected. Pigments are combined to form different colors by a process of subtractive absorption of various wavelengths.