MIT and Microsoft researchers demonstrated a system of gold leaf temporary tattoos for "on-skin user interfaces" including a touch sensor, near field communication antennae, and a low-res thermochromic display that changes color. From the research description:
DuoSkin draws from the aesthetics found in metallic jewelry-like temporary tattoos to create
on-skin devices which resemble jewelry. DuoSkin devices enable users to
control their mobile devices, display information, and store information on
their skin while serving as a statement of personal style. We believe that in the
future, on-skin electronics will no longer be black-boxed and mystified; instead,
they will converge towards the user friendliness, extensibility, and
aesthetics of body decorations, forming a DuoSkin integrated to the extent that
it has seemingly disappeared.
DuoSkin (MIT)