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 Fornula 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 carboxymethyl