This example illustrates the preparation, by reactions analogous to V ??? W ??? X shown in FIG. 5, of the dye of Formula N (FIG. 3) in which R3 is a carboxymethylamino group and R1 and R4 are each a hydrogen atom, this being the dye of Formula I in which Q1 is a 2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene grouping, Q2 is a 2,6-bis-[1,1-dimethylethyl]thiopyrylium grouping, R3 is a carboxymet