The first page from the luxurious shunga book The Secret Lovers (Shinobu-zuri) Vol.1, depicting a close-up portrait of an oiran wearing an uchicake outer robe decorated with morning glories.

The production of such multicoloured erotic books was considered overindulgent luxuries and was forbidden due to the sumptuary laws of the time. However, illicit shunga books continued to be secretly published and distributed. Unlike books printed in black and white, multicoloured printing required thicker, higher-quality paper. Additionally, deeply saturated colours were achieved by repeated printings of the same colour printing blocks and the lavish use of expensive pigments.