What's that green stuff? Is the coating wearing off?
If you look at other pictures of that aircraft, it seems like this is a prototype that they'd applied a coating on somewhat partially -- the trailing edge flaps of the wings also show a thin line of the exposed green primer below.
Either it's a prototype that was flown very thoroughly, or it's a prototype that was only recently painted possibly for purposes of the air show.
Regardless, there's not too much to read into, and I am not sure I would call it a "coating" because that implies it is covered by some sort of RAM.