The present invention relates to a process for preparing surface-modified colored pigments. The process includes the steps of: preparing a reaction batch comprising a treating agent and a diazotizing agent; adding a colored pigment to the batch; and mixing the colored pigment and the batch under high shear conditions to form a reaction product comprising a surface-modified colored pigment. The treating agent has an organic group which comprises at least one diazotizable group. In a prefered embodiment the diazotizable group comprises a) at least one aromatic group or at least one C1-C20 alkyl group, and b) at least one ionic group, ionizable group, nonionic group, or a mixture thereof. The surface-modified colored pigments prepared by the process of the present ivention have been found useful in aqueous or solvent based compositions and particularly in ink jet ink compositions.