The Galaxy color-magnitude diagram shows the relationship between absolute magnitude, luminosity, & mass of galaxies. A preliminary description of the areas of this diagram was made in 2003 by Eric F. Bell et al. from the COMBO-17 survey[1] that clarified the bimodal distribution of red & blue galaxies as seen in analysis of Sloan Digital Sky Survey data[2] & even in de Vaucouleurs' 1961 analyses of galaxy morphology[3] Noticed in this diagram are main features: the red sequence, the green valley, & the blue cloud. The red sequence includes most red galaxies which are usually elliptical galaxies. The blue cloud includes most blue galaxies which are usually spirals. In between the distributions is an underpopulated space known as the green valley which includes plenty of red spirals. Unlike the comparable HertzsprungRussell diagram for stars, galaxy properties are not necessarily determined by their location on the color-magnitude diagram. The diagram also shows considerable evolution through time. The red sequence earlier in evolution of the universe was more constant in color across magnitudes & the blue cloud was not as uniformly distributed but showed sequence progression.