Hi Jengjeng! I just finished building their 1/144 F-14 (the one with the flight deck and fire truck) I built it with the gear up and on a clear plastic rod. Anywho, I know Navy planes are very well maintained because it they're not then corrosion can set in. In spite of that, I wanted to depict mine as a rather well used aircraft. I took a fine chiseled brush and EVER SO GENTLY tamped in some reddish-brown pastel chalk. I did it gently because I then 1)blew off the excess, and then 2)took a very soft brush and brushed away whatever was still left on after the blowing. What was aleft was a fine brown tinted panel line. I tried it first (not knowing how it would turn out) on the bottom of the plane where it might be hidden if I really glitched things up. But I was so happy with the result that I did the whole plane that way. Let us know how your plane turns out!
Oh, to also simulate the many paint touch-ups that Navy planes endure I took a piece of paper towel, crumpled up an end, and stippled the plane with a slightly darker shade of the plane's original color. It looked like a bit of a contrast so I then went back and air brushed an extremely thinned coat of the base color on it to gently blend the two colors. Hope this all helps.
Eric