complementary

Adjective

• acting as or providing a complement (something that completes the whole)

• of words or propositions so related that each is the negation of the other
  • `male' and `female' are complementary terms
    

Noun

• either one of two chromatic colors that when mixed together give white (in the case of lights) or grey (in the case of pigments)
  • yellow and blue are complementaries
    

Related words

• Synonyms: 
  complemental , completing , complementary color