transformers-extrication:

This is a gif of a ‘concept car’ by BMW called “The Vision” 

And this is how I Cybertronian skin looks under a high-power microscope.

The way it can ‘stretch’ out occasionally gives an accidental illusion of a Cybertronian changing size, obviously not by much but during transformation it’s juuust enough to make you look twice. Obviously they do not change size.

Underneath the outer layer, Cybertronians do have a ‘light’ layer where natural luminescence shows through, the pattern and shape consistent with how their skin stretches and shrinks. The ‘light layer’ does not reach all over the body and the individual can only ‘flash’ one colour, being able to flash and show these lights evolved into it’s own mini-language and emotional response. However, due to the war no Cybertronian has revealed their light layer in eons as a glowing target is an easy target.
So in a way their ability to show light is similar to how cephalopods change colour.

To the touch it feels smooth yet bumpy, like an odd mix between chain-mail and snakeskin.
Mirage’s skin and luminescence are highly evolved allowing him his invisibility power, his skin occasionally lightly changes texture too in order to provide better cover.

A Cybertronians light layer shuts off and goes out when they die, combine this with the skin failing and their ‘paint’ thinning it makes them turn ‘greyscale’ as they die.