Well, it's only paintabe for Scout (the undershirt, to be precise), but not for Heavy and Sniper. The creator has explained why (https://www.reddit.com/user/SedimentarySocks), but I was thinking how it could be painted for all classes.

For Sniper, those team-colored strips the jacket has in the arms could be paintable, perhaps it could be quite a nice contrast as well.

For Heavy, I don't really know, since the only difference of team in the jacket's color is the arm strip, but perhaps, one strip could be paintable, and the other stay as a team color? I wouldn't really know.

Well, hopefully SedimentarySocks takes this into consideration. Not saying this is the best idea in the world, nor that they are obligated to do this, but I think this would be a nice way to paint the jacket in Hoovster and Snoipah.