We can represent most colors in the visible spectrum by mixing the three primary colors: red, green, and blue (RGB). When the three primary colors overlap, they create the (subtractive) secondary colors: cyan, magenta, and yellow.
Since the primary colors combine to create white, they are also called additive colors. Adding all the colors together creates white - that is, all the light is reflected back to the eye. Additive colors are used for lighting, video, film recorders, and monitors. Your monitor, for example, creates color by emitting light through red, green, and blue phosphors.