We know from our observation of rainbows that visible light (white light) is composed of a continuum of colors from violet to red. If a beam of white light is passed through a beaker of water, it remains white. If potassium permanganate is added to the water, the white light appears purple after it passes through the solution. The permanganate solution allows the red and blue components of white light to pass through but absorbs the other colors from the original beam of light.