Newton thought that color is infused by pressure on the eye. To prove this, in an optical experiment, Newton stuck a darning needle around the side of his eye until it poked the backside.
He calmly noted that he saw white, dark, and colored circles when he stirred the needle in his eye. Although it is not known what he concluded from his experiment, Newton argued that light is composed of particles.
Science later adopted a wave theory of light and color, because of what some experiments found. Newton had some vindication on his theory, though. With the discovery of quantum mechanics, light is now thought to be both a wave and a particle.