The galaxy color–magnitude diagram shows the relationship between absolute magnitude (a measure of luminosity) and mass of galaxies. A preliminary description of the three areas of this diagram was made in 2003 by Eric F. Bell et al. from the COMBO-17 surveyBell, Eric F. et al. Nearly 5000 Distant Early‐Type Galaxies in COMBO‐17: A Red Sequence and Its Evolution since z=1, The Astrophysical Journal, 608:752–767, 2004 June 20. that clarified the bimodal distribution of red and blue galaxies as seen in analysis of Sloan Digital Sky Survey dataStrateva, I., et al. Color Separation of Galaxy Types in the Sloan Digital Sky Survey Imaging Data, 2001, The Astronomical Journal, 122, 1861 and even in de Vaucouleurs's 1961 analyses of galaxy morphology.de Vaucouleurs, G. Integrated Colors of Bright Galaxies in the u, b, V System. 1961, The Astrophysical Journal Supplement Series, 5, 233.
