Complementary colors

from The Collaborative International Dictionary of English v.0.48

Complementary \Com`ple*men"ta*ry\, a.
   Serving to fill out or to complete; as, complementary
   numbers.
   [1913 Webster]

   {Complementary colors}. See under {Color}.

   {Complementary angles} (Math.), two angles whose sum is
      90[deg].
      [1913 Webster]