When was red green color blindness discovered?

Red-green color blindness, also known as deuteranopia, was first discovered in 1794 by the English chemist John Dalton. Dalton was interested in the phenomenon of color blindness, and he conducted experiments on himself and his friends to study how they perceived colors. He noticed that he and several of his friends had difficulty distinguishing between red and green objects, and he concluded that they were red-green color blind.

Dalton's discovery was important because it was the first time that color blindness had been scientifically studied and characterized. He published his findings in a book titled "Extraordinary Facts Relating to the Vision of Colours," which is considered a landmark work in the field of color vision research.