Meaning of alkali blue

al'kali blue'

Pronunciation: [key]
— Chem. Chem.
  1. any of the class of blue pigments having the highest tinting strength, by weight, of all known blue pigments: used chiefly in the manufacture of printing inks.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.