/ Dictionary / Index C color index: Meaning and Definition of Find definitions for: col'or in"dex Pronunciation: [key] — Astron. Astron. the difference between the apparent photographic magnitude and the apparent visual magnitude of a star. 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. colorimeter coloring Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language