Christine Ladd-Franklin (1847-1930) was an American psychologist, logician, and mathematician. She was the first woman to receive a Ph.D. in mathematics and logic (in 1882), although the degree was not officially granted to her by Johns Hopkins University until 1926 (44 years after she had earned it) because of discrimination. One of the major contributions that Ladd-Franklin made to psychology was her theory of color vision, which was based on evolution. Ladd-Franklin concluded that color vision evolved in three stages: achromatic vision (black and white), blue-yellow sensitivity and red-green sensitivity. Since red-green sensitivity was the last to evolve it explains why many people suffer from red-green color blindness. Her principal works are The Algebra of Logic (1883), The nature of Color Sensation (1925), and Color and Color Theories (1929). Ladd-Franklin was also a prominent member in the women's suffrage movement.