2,​7-​Naphthalenedisulfoni​c acid, 5-​[[4-​chloro-​6-​[(4-​methyl-​2-​sulfophenyl)​amino]​-​1,​3,​5-​triazin-​2-​yl]​amino]​-​3-​[2-​(4,​5-​dimethyl-​2-​sulfophenyl)​diazenyl]​-​4-​hydroxy-​, sodium salt (1:4)