Programmable Tattoos.

Squid and octopus can change their skin to blend into their surroundings - in the future, with the help of nanotechnology, maybe humans too can have programmable tattoos:

This "dermal display" (featured on the winter 2006 cover of Cryonics magazine) would consist of about three billion light-emitting nanorobots capable of rearranging themselves to spell out words and numbers and produce animations for the display. To turn on and control the display, you simply tap it with your finger.

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