The Collaborative International Dictionary of English v.0.48:

magenta \ma*gen"ta\ (m[.a]*j[e^]n"t[.a]), n. (Chem.)
   An aniline dye obtained as an amorphous substance having a
   green bronze surface color, which dissolves to a shade of
   red; also, the color; -- so called from Magenta, in Italy, in
   allusion to the battle fought there about the time the dye
   was discovered. Called also fuchsin, fuchsine, roseine,
   etc.
   [1913 Webster]

   2. The purplish-red color of magenta.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Roseine \Ro"se*ine\ (? or ?), n.
   See Magenta.
   [1913 Webster]