This Example illustrates the preparation of the dye A (FIG. 2) in which R3 is a toluenesulfonyl grouping and R1, R2 and R4 are each a hydrogen atom (this being the dye of Formula I in which Q1 is a 2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping, Q2 is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium] grouping, R3 is a toluenesulfonyl grouping and R1, R2 and R4