 In aqueous solution large numbers of Alcian blue molecules stack together as micelles of very large size, too large to be even dialysed.Thus even at a fairly high dilution, it has an absorption maximum at ~600–615 nm, which is actually not the absorption maximum of a dye monomer but that of the multimer.Since the absorbed light is of yellow orange spectrum, the transmitted/reflected light is perceived by our eye as the complementary color of slightly greenish blue or cyan.