The greatest shapeshifter in the world

In the third episode of Season 3, Supergirl and J'onn J'onzz go to Mars, the red planet.

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The Martian Manhunter was created in 1955, at the beginning of the silver age of superheroes, by Joseph Samachson and Joe Certa on the page of Detective Comics #225. He is a variation on the myth of the little green men. The first use of a little gren-skinned extraterrestrial form of life was found by Chris Aubeck in the tale Green Boy From Hurrah (1899) and he found the first use of the phrase little gren man referred to martians in the Daily Kennebec Journal (1908). In 1912 in the science fiction novel A Princess of Mars, Edgar Rice Burroughs described martians about at 10 to 12 feet tall that are not so little.
There's also an astronomical curiosity about the term:

In 1967, Jocelyn Bell Burnell and Antony Hewish of the University of Cambridge, UK dubbed the first discovered pulsar LGM-1 for "little green men" because the regular oscillations of its signal suggested a possible intelligent origin. Its designation was later changed to CP 1919, and is now known as PSR B1919+21.

But J'onn is not only green, but also a shapeshifter. From a biological point of view, this superpower is a bit complex, because J'onn's cells must have shapeshifter genes and use a very great number of shapeshifter proteins. There's also the conservation of mass law that create some problems to the shapeshifter, because it must change is shape without change mass: this is a limitation to what kind of shape and object that could be "played" by the shapeshifter.
But from a technologicaly point of view the problem seems more simple:

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via BGR

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Pikul, J. H., Li, S., Bai, H., Hanlon, R. T., Cohen, I., & Shepherd, R. F. (2017). Stretchable surfaces with programmable 3D texture morphing for synthetic camouflaging skins. Science, 358(6360), 210-214. doi:10.1126/science.aan5627
Read also: Verduzco, R. (2015). Shape-shifting liquid crystals. Science, 347(6225), 949-950. doi:10.1126/science.aaa6579