ormula (b) preparing a second reaction mixture by admixing (1) the alcohol-substituted colorant, (2) an isocyanate of the formula R4???N???C???O wherein R4 is an alkyl group, an aryl group, an arylalkyl group, or an alkylaryl group, and (3) an optional catalyst and heating the second reaction mixture to form a urethane-substituted colorant of the formula and (c) forming a third reaction mixture by