- astronomy the difference between the apparent magnitude of a star measured in one standard waveband and in a longer standard waveband, indicating its colour and temperature
- geology the sum of the dark or coloured minerals of a rock, expressed as a percentage of the total minerals
- chem physics a systematic arrangement of colours according to their hue, saturation, and brightness
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Examples from the Web for colour index
Instead of s there may also be used another expression for the colour, called the colour-index.
The difference between the photographic and the visual magnitudes is called the colour-index (c).
From each catalogue of visual magnitudes of the stars we may obtain their photographic magnitude through adding the colour-index.