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How did Isaac Newton’s prism experiments show that white light contains many colours?

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A circular RYB color wheel divided into twelve segments, showing a progression of colors from red, orange, and yellow to green, blue, and violet. — colour The RYB color model is being illustrated on a color wheel.

Isaac Newton’s experiments in 1665 and 1666 fundamentally changed the scientific understanding of light by replacing the ancient theory of "modification"—which suggested white light was pure and colors were merely altered versions of it—with the concept of analysis.1

Newton demonstrated that white light is not simple or homogeneous, but rather a complex, heterogeneous mixture of rays. By passing a narrow beam of sunlight through a prism, he observed that the light dispersed into a spectrum of distinct colors. He concluded that this occurred because individual rays of light possess immutable properties and refract at distinct angles when passing through the glass. Specifically, shorter wavelengths (toward the violet end) are refracted more than longer wavelengths (toward the red end).123

Newton further proved this by showing that these separated spectral bands could be recombined through a second prism to recreate the sensation of white light. This discovery of the heterogeneity of light established the foundation for modern physical optics.41