ABSTRACT In the years after 1870, two theories of color vision vied for primacy: the “trichromatic” theory and a four-color theory, also known as an “opponent” theory of color vision. Among scientists who participated in this debate, mathematician Christine Ladd-Franklin (1847–1930) made special use of graphics as a rhetorical template for reasoning and explanation. Her later work included figures modeled upon novel graphic representations of logical relationships to describe chemical reactions fundamental to visual processes. These and other illustrations demonstrate, in retrospect, how innovation in graphic notation can underlie shifts in the practice and perception of science.