Just finished this painting today. It was inspired by a cover photo on an old Australian Geographic, which just screamed out WATERCOLOUR!
Iridophores lie beneath the chromatophores and contain multiple tiny platelets that reflect light, producing the iridescent and metallic colours. Beneath the iridophores are leucophores, which reflect the predominant light in the environment (i.e., they appear white in white light, blue in blue light etc.). Besides the very impressive colour displays, cuttlefish are able to add another dimension to their camouflage, by creating protrusions in their skin with papillae, they can also mimic textures as well as colours.