The Collaborative International Dictionary of English v.0.48:

Colorist \Col"or*ist\, n. [Cf. F. coloriste.]
   One who colors; an artist who excels in the use of colors;
   one to whom coloring is of prime importance.
   [1913 Webster]

         Titian, Paul Veronese, Van Dyck, and the rest of the
         good colorists.                          --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

colorist
    n 1: a painter able to achieve special effects with color