A method of coloring a substrate is disclosed that includes the steps of dissolving a vegetable oil ester based solvent wherein the ester is selected from a group consisting of esters having carbon chain length of C-1 to C-18 in a liquid solvent dye to form a low-sulfur containing dye formulation such that the vegetable oil ester is present in an amount of between about 5 and 80 percent by weight of the dye formulation, and mixing sufficient amounts of the dye formulation with the substrate to produce mixtures of predetermined color in which the levels of toxic substrate are substantially less than in otherwise equivalent mixtures that include hydrocarbon-based solvents.