Specific preferred leuco dyes of Formula V are those in which each R6 is a methyl group, and each R7 is a o-chlorophenyl group, or each adjacent R6 and R7 together with the intervening nitrogen atom forms an indolinyl group; Y is an SO2 group; and Q and P together form an --(o--C6 H4)--NH--C(???O)--O--C(???CH2)CH3 group.