Aobana is a colorant that originated in Japan and that has been in use for years.
Aobana, literally meaning blue flower, is obtained from the petals of perennial plants such as tsuyukusa (blue dayflower) and hotarugusa (firefly grass). The blue liquid is then applied to a paper which acts as a carrier for the colorant. Aobana is therefore called aobana-gami (aobana paper) or ai-gami (indigo paper) on some occasions. Aobana colorant has been used to draw rough sketches, most often for sketching Yuuzen patterns.
If you tear a small amount of aobana, place it on a plate and pour some water over it, the blue liquid will appear. This aobana colorant appears only on contact with moisture which makes it an ideal colorant for sketching.
The fleeting nature of aobana has been well recognized since ancient times, which is evidenced by an old waka poem: “people’s minds are like the elusive blue dayflower that changes its color easily”.