What makes galaxies the colors that they are?

The color of a few galaxies is affected by distance; an extremely distant galaxy has a high recessional velocity due to the expansion of the universe, which causes its light to be shifted toward the red (google "relativistic Doppler shift"). read more

Here are a few colors you might see in galaxy images, and what they're usually caused by: Blue: a region with many young stars. High-mass stars live fast and die young, using fuel at a high rate to maintain high temperatures. read more

Generally, galaxies divide into "red" and "blue". These colors reflect the rate at which new stars are forming. Blue galaxies have ongoing star formation, while red galaxies have not had any new star formation for some time. Blue galaxies also tend to have a spiral structure, while red galaxies tend to be more like elliptical blobs of stars. read more

Galaxies are moving away in all directions at an incredible speed as the universe expands. Since they are moving away from us at different speeds, some of them appear to shift color. (The frequency of the light reaching us is reduced because of the speed.) This makes some galaxies (and stars) appear red. this is called “red shift”. read more