chromophore

from WordNet (r) 3.0 (2006)

chromophore
    n 1: the chemical group that gives color to a molecule

from The Collaborative International Dictionary of English v.0.48

Chromophore \Chro"mo*phore\, n. [Gr. ? color + fe`rein to bear.]
   (Chem.)
   Any chemical group or residue (as {NO2}; {N2}; or {O2}) which
   imparts some decided color to the compound of which it is an
   ingredient.
   [1913 Webster]