Purpose: In this paper the chromatic contrast was defined as color difference CIEDE2000, the sensitivity was defined as reciprocal of threshold of the color difference, and the CSFs called color difference sensitivity functions were measured. Methods: The CSFs of 4 subjects were measured for nine spatial frequencies(0.28, 0.56, 1.00, 1.97, 2.95, 4.72, 6.74, 11.80 and 15.74cpd) gratings of mean luminance of 40cd/m2 on a CRT display. Measurements were made for gratings whose average color was a chromatically neutral point(a*=0 and b*=0) and also for modulations around four chromatic points along the color directions a* and b* in the CIELAB color space. Results. The thresholds of color difference are from 0.74 to 6.67 in the range of experimental frequencies. The color difference sensitivity functions are similar with known results that CSF curves for the two chromatic directions are consistently low-pass irrespective of the average color of the stimulus. The sensitivity to gratings for b* direction is identical as for a* direction below spatial frequency 4.72cpd, however, the sensitivity for b* direction is smaller than the one for a* direction above spatial frequency 4.72cpd, which indicates that the CIEDE2000 threshold for grating with lower frequencies(i.e., small color differences) is not related to the chromatic direction and chromatic point of modulation, however, the threshold is related to the chromatic direction and chromatic point of modulation for large color differences.