Chapter 4 129 The reaction scheme displayed in Eqs. 6 and 7 shows the stages involved in color formation. Oxidation of the primary intermediate to form a diimine Eq. 6 Reaction with the coupler and further oxidation of the leuco dye to the colored dye. Eq. 7 In the reaction above, only the bi-nuclear dye is formed because the second coupling position is “blocked” by the methyl (CH 3 ) group. In Table 3 a selection of some other reaction products are shown, including some “unblocked” couplers, which form tri- nuclear dyes. These trinuclear dyes can often undergo additional polymerization to form a “bigger” conjugated system. Thus these dyes are often very wash resistant but do not form vibrant tones such as blues and reds.