In 1666, the English scientist Isaac Newton found that white light from the sun is actually composed of lights of various colors.
This can be noticed when white light passes through a glass prism. Under these conditions the decomposition of white light occurs in the various colors that make up the rainbow.
Although it is popularly said that the rainbow has seven colors - red, orange, yellow, green, blue, indigo and violet - in reality it has numerous distinct colors that include many shades of red, orange, yellow, green , blue (including what used to be called indigo) and violet.
When all these colors simultaneously reach the human eye, they cause the visual sensation of white light. To demonstrate this, Newton painted a disc with rainbow colors and set it in rapid rotation. In this experiment, known as newton disc, the eye begins to see the disc with the color white, the result of the "mixing" of the rainbow colors.
Newton's Disc Experiment
A long time has passed since Newton experimented with light. Scientists now know much more about colors and how the human eye sees them than was known at the time.