color index

noun Astronomy.

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.

Origin of color index

First recorded in 1920–25

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for color index

Historical Examples of color index

The color-index is thus almost invariably low, the average being about 0.5.
A Manual of Clinical Diagnosis
James Campbell Todd