A disc with segments in rainbow colors, when rotated at high rpm will project a near white gray color. The optical mixing of the colors demonstrate that white light is a combination of the seven colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. A gray color rather than a pure white color is produced due to the phenomena known as ADDITIVE-AVERAGING MIXING.
Early examples of Newton's Disc at the Virginia Military Institute in Lexington, Virginia and the National Museum of American History at the Smithsonian show a disc made of transparent segments to be mounted on a lantern .
REF: Thomas B. Greenslade, Jr., "Spectrum Recombination", Phys. Teach., 22, 105-108 (1984)
References
Newton disc Wikipedia(Text) CC BY-SA