In this work we create a computational model, which assesses chromaticity differences based on an ellipse data set. The used ellipse data sets are the MacAdam ellipses in the CIE 1931 (x,y)-chromaticity diagram and the ellipses which were used to derive the CIEDE2000 color-difference formula in the CIELAB color space. In general the ellipse data set can be any set of planar chromaticity ellipses. The chromaticity differences are calculated from the surfaces which are defined by the ellipse data set and the two chromaticity points whose the chromaticity difference is calculated. The distances along the surfaces are calculated by a method based on the Weighted Distance Transform On Curved Space (WDTOCS). The computational model corrects the planar values in chromaticity difference calculation.