Light is electromagnetic radiation that is in the form of a wave. Each wave has a wave length or frequency. The human eye sees each frequency as a different color. Rainbows show the entire spectrum of visible light. The separate colors, moving in from the outer edges, are usually listed as red, orange, yellow, green, blue, and violet. Other colors can be seen only with special cameras or instruments: outside of red is infrared, and inside of violet is ultraviolet.
Light and color are forms of analog information. However, electronic cameras and computer displays work with digital information. So, electronic cameras or document scanners make a digital version of a color image by separating out the full color image into separate red, green, and blue images. Later, a digital display uses pixels of just those three colors. Computer screens use only these three colors in different brightness levels. The brain combines them to see all of the other colors in the image.
People think of objects as having color. Scientist explain this because the molecules that make up the object absorb certain light waves, leaving the other light waves to bounce off. The human eye sees the wave lengths of all of the light that was not absorbed, and the combination of those leaves the brain with the impression of a color.