When a sound source is moving away from you, the pitch becomes lower, indicating a decrease in perceived frequency. If a light source is moving away from you very quickly, its perceived frequency also decreases. This perception of decreased frequency alters the color of the light. Which end of the visible light spectrum would you expect the color of the light to shift toward?

red

Explanation:

When the source of light moves away or comes closer to an individual, the wavelength of the light decreases or increases respectively and the color of the light changes slightly in what is known as the doppler effect.  

When the light source moves towards an individual, the wavelength shifts towards the blue end of the spectrum, and the phenomenon is known as the blueshift. When the source of light moves away from an individual, the wavelength shifts towards the red region of the spectrum, and the phenomenon is known as the redshift.