One of Isaac Newton's major discoveries was that white light is actually composed of colors. Prior to this discovery, which he proved through experimentation with prisms, it was believed that white light was the purest form of light.
One of Newton's biggest contributions to the field of optics is the foundational concept that white light is heterogeneous; that is, white light is composed of colored light (red, orange, yellow, green, blue and purple). The image of a beam of white light splitting into colors is not novel in the modern world; even major rock bands in the 1970s used this image. In his day, however, Newton's discovery was a major revelation.