It's difficult to pinpoint a single "first person" to discover the existence of color in light, as the understanding of light and color developed over centuries through the work of many individuals.

However, a significant figure in this journey is Isaac Newton.

In 1666, Newton conducted his famous experiment with a prism, demonstrating that white light is actually composed of a spectrum of colors. This experiment, known as Newton's prism experiment, was a crucial step in understanding the nature of light and color.

Before Newton, people had observed the rainbow and other color phenomena, but Newton's work provided a scientific explanation for these observations.

While Newton wasn't the first to observe color, his experiments helped to solidify the understanding that color is a property of light itself, not an inherent property of objects.