That's an interesting question. For thousands of years, people thought that our eyes emit some sort of ray that senses the presence of objects around us. It was Egyptian physicist Alhazen (965-1038) who first realized that our eyes observe passively and that we see light that comes to us from sources outside ourselves.
What we see is the light that comes toward us from objects in our environment. That light either originates directly in those objects (e.g. the sun) or is redirected by them from elsewhere so that it travels toward our eyes (e.g. the moon). The colors we see when we look at objects are due partly to the colors of the light sources and partly to variations in the ways those objects redirect light from elsewhere.
Answered by Lou A. Bloomfield of the University of Virginia