| http://www.w3.org/ns/prov#value | - Particularly preferred as color developers are N,N-dialkyl-p-phenylenediamines, of the general formula wherein each of R 1 and R 2 , independently of the other, is an alkyl group, preferably with from 1 to about 4 carbon atoms, or a substituted alkyl group, wherein the benzene ring can be substituted, and wherein 2 or more substituents can be joined together to form additional rings.
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