What I do in situations like this...... get a scrap peice of plastic, preferably the same color as the model, prime it (if you do) and spray different colors (aircraft gray, light ghost gray, ect) and compare to photos. I don't think that it has to be the exact shade of gray....unless your a nit-picky guy. But if your doing an X-Wing as they were in the starting years of the Alliance, I think they had that haggard, hand-me-down look to them.
LOL the fit problem...... try the Star Destroyer.......bloody nightmare......
Cheers