What is the hue of rod vision?

Textbooks say rod vision is colorless. However, evidence that rod signals influence hue comes from several lines of psychophysical studies, including scotopic color contrast, color matching, hue scaling, and unique-hue loci. Some widely cited early studies suggested that there is a single rod hue, which is blue. Other studies have suggested that various other hues, or even all hues, can be associated with rod stimulation This article presents a conceptual frame work that helps reconcile many of these findings and that involves two unifying generalizations. (1) Rod signals are associated with signals from all three cone types and have a ubiquitous influence on all portions of the color pathways. (2) But rod signals have multiple inherent biases (differential weightings) in their effects on color pathways, and the "net effect" of these individual biases is often found to be blue. The multiple rod influences on hue, and their net blue influence, may have a basis in the parallel pathways that are the retinal substrate of color vision, (C) 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S57-S59, 2001.