Red is a basic color. The work of Kay and Berlin on the evolution of color names in languages shows that, after white and black, red is the most basic of color terms. Red plays a key part in Hering's color opponent theory, and is one of the elementary colors in both the Munsell Color system and in the Natural Colour System (NCS). The CIELAB color system has an axis which is sometimes referred to as the red-green axis. But unique red is about 25 degrees degrees counterclockwise from the positive a* axis. This article answers the question of why this is.