The color black usually signals the absence of light. But inside the solar system, space is filled with light.



“Light usually travels straight ahead in a line unless it reflects off of something or is bent by a lens,” explains Geza Gyuk, Director of Astronomy at the Adler Planetarium and a research scientist at the University of Chicago.
Think about how you can see the spot of a laser pointer but not the beam. “The light that makes up the beam just goes ahead to where the pointer is pointing and not to where your eye is,” Gyuk said. “So even though space may be full of light, none makes its way to your eye unless you are looking at something bright.”
So, Gyuk said, “Because most of the universe is empty, outer space looks black.”