Meaning of color index

col'or in"dex

Pronunciation: [key]
— Astron. Astron.
  1. the difference between the apparent photographic magnitude and the apparent visual magnitude of a star.
  2. the difference between the magnitudes of a star in any two spectral regions.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.