Abstract: In contrast to luminance contrast detection, the paper studies the characteristics of human chromatic contrast detection (contrast detection based on changes in chromatic distribution over space). Based on a detailed analysis of previous works, the paper utilizes fundamental colorimetry principle to analyse the luminance, dominant wavelength and colorimetric purity variance of the red green and yellow blue gratings. It then presents a new theory for color contrast detection, and indicates that the isoluminant contrast sensitivity function can similarly be described by the luminance contrast, dominant wavelength, and colorimetric purity. Thus some part of the chromatic vision experimental characteristics can be explained. Furthermore, this three chromatic contrast provides a possible way for color image evaluation.