Pyridinium, 1,1'-[(6,13-dichloro-4,11-disulfo-3,10-triphenodioxazinediyl)bis[imino-2,1-ethanediylimino[6-[(2,5-disulfophenyl)amino]-1,3,5-triazine-4,2-diyl]]]bis[3-carboxy-, dihydroxide, bis(inner salt), hexasodium salt