Abstract: A process for the production of a tinted polymer, which comprises co-polymerising a compound of the general formula I or a salt thereof with a polymerisable monomer containing a vinyl group, formula I being: in which R represents a hydrogen atom or an —SO3H group; A represents a direct bond, -alkylene-O—, or a -phenylene-NH— or -phenylene-NH-phenylene-NH— group in which the or each phenylene ring may be optionally substituted by one or more of the same or different groups selected from —SO3H, —(CH2)mSO3H, —SO2(CH2)mSO3H, —SO2NH(CH2)mSO3H, —SO2C1-2alkyl, —SO2C1-2haloalkyl, —SO2NHC1-2alkyl, —SO2NHC1-2haloakyl, —C1-2alkyl, or C1-2haloalkyl, in which m represents 1 or 2; R1 represents a hydrogen or halogen atom or a C1-4 alkyl group; and each of R2 and R3, which may be the same or different, represents a hydrogen atom or a C1-4 alkyl or alkoxy group; with the proviso that, if R1 represents a hydrogen or a C1-4alkyl group and simultaneously R represents a hydrogen atom, A must represent a -phenylene-NH— or -ph