I deal with repaints and uploads every day. In 10's 1000's of uploads and many years -- I can count on 1 hand the number of times there has been a problem.
Freeware aircraft - OK to upload either textures or whole aircraft. If you are in doubt you can always contact the original designers, which is often not really possible. In almost all cases they will give you the OK and be pleased that someone has done another repaint.
Simplicity is the ultimate sophistication. – Leonardo da Vinci