My bad, i thought that was the turtleneck of the shirt.

Anyways, i tried to ask Texman(One of the creators), and they told me its the scarf that is paintable, the third spy loadout appears to have a slightly lighter red scarf than the rest, while the unpainted ones seems darker.

Actually that's a different coat shown painted. I believe it's the "Le Professionnel"

@BoxernBuffa
Judging by the Spy on the right in the last picture, i'm gonna assume its the inner shirt.

what's the paint region?

Looks great! Would a plain style be too much to ask?