Since the 1976 provisional recommendation of the CIELAB and CIELUV uniform color spaces and color difference formulae, a Committee of the Commission Internationale de l'Eclairage (CIE) has continued to work on the problem of color difference evaluation. In 1978 the committee published some guidelines in an effort to stimulate and coordinate research in the area. Following that, a number of studies were undertaken in which color difference ellipsoids were derived from observations of object colors. These studies have measured the effect (or lack of effect) of parameters such as the size of the color difference, the severity of the observer, and the type of dividing line between the samples. Other studies have shown that different relative weights for lightness, chroma, and hue indices may be needed for different viewing conditions and for different types of sample. Work planned for the next four years includes an attempt to assemble a single representative set of data with which color difference formulae can be tested.