Color-based object indexing and matching is attractive because color is an efficient visual cue for characterizing an object. However, different light sources will lead to color deformation of objects, which will inevitably degrade the performance of recognition. In order to circumvent this confounding influence, we present three effective illumination-independent descriptors that are substantially insensitive to the variations of light conditions, object geometric transformation, and image blur level. To this end, we define two new two-dimensional color coordinate systems, the central color coordinate system and the edge-based color coordinate system, based on the diagonal-offset reflectance model. By introducing normalized moment invariants, this paper then provides two color-constant descriptors in each system separately. Either descriptor is a feature vector consisting of several normalized moment invariants of the color pixels' distribution with different orders. Furthermore, the combination thereof can characterize not only color content but also color edges in an image, so it serves as a third descriptor of the image. Experiments on real image databases with object recognition and image retrieval show that our descriptors are robust and perform very well under various circumstances.