A series of colorants permitted in food products, marking inks, etc., certified by the FDA. Among the more important are the following: Blue No. 1: disodium salt of 4-((4-(N-ethyl-p-sulfobenzylamino)-phenyl)-(2-sulfoniumphenyl)-methylene)-(1-(N-ethyl-N-p-sulfobenzyl)-Δ2,5-cyclohexadienimine). Blue No. 2: disodium salt of 5,5′-indigotin disulfonic acid. Green No. 3: disodium salt of 4-((4-(N-ethyl-p-sulfobenzylamino)-phenyl-(4-hydroxy-2-sulfonium phenyl)-methylene)-(1-(N-ethyl-N-p-sulfobenzyl))-Δ2,3-cyclohexadienimine). Green No. 6: 1,4-di-p-toluidinoanthraquinone. Red No. 2: trisodium salt of 1-(4-sulfo-1-naphthylazo)-2-naphthol-3,6-disulfonic acid. Formerly the largest volume food color in commercial use. A carcinogen. Use prohibited by FDA. Red No. 40 is currently a permissible substitute. Red No. 3: disodium salt of 9-o-carboxyphenyl-6-hydroxy-2,4,5,7-tetraiodo-3-isoxanthone (erythrosin). Red No. 4: disodium salt of 2-(5-sulfo-2,4-xylylazo)-naphthyl-4-sulfonic acid. Use in foods prohibited by FDA. Violet No. 1: monosodium salt of 4-((N-ethyl-p-sulfobenzylamino)-phenyl)-(4(N-ethyl-p-sulfoniumbenzylamino)-phenyl)-methylene)-(N,N-dimethyl-Δ2,5-cyclohexadienimine). Use prohibited by FDA in 1973 and by USDA in 1976. Yellow No. 5: trisodium salt of 3-carboxy-5-hydroxy-1-p-sulfophenyl-4-sulfophenylazopyrazole. Yellow No. 6: disodium salt of 1-p-sulfophenylazo-2-naphthol-6-sulfonic acid.See Food Color; Food Additive.