In some examples, a plurality of print material combinations for object generation are determined, each print material combination having an associated color. A plurality of color descriptions may be determined, the color descriptions corresponding to a combination of voxels, each of the voxels of the combination of voxels having a defined print material combination and a defined depth with respect to a surface. A color mapping resource may be defined, the color mapping resource associating a color description with a print instruction, each print instruction being for use in causing an object generation apparatus to generate the combination of voxels corresponding to the associated color description.