In many cases, the synthesis of the final aminosquarylium dye is most simply achieved by introducing the final NR3 R4 group during the preparation of the compound L; for example, when each of R3 and R4 is a hydrogen atom or an alkyl group, so that the compound HNR3 R4 is ammonia or a primary or secondary amine, the reaction K ??? L proceeds well with ammonia or a primary or secondary amine so that