Jankees thanks for your reply, yes I saw the white textures inside the airplane installation folder but it is so hard to do a repaint from it.
I used to work from a complete fuselage for repaint some airplane like Airbus A340/A330 et Boeing 787-8 or -9.
Matt, would it be possible to share your base texture files or technics to do a repaint from those ATR white texture?