YELLOW!
As we all know, yellow is tough to paint, and you seem to have pulled this one off very well.

There seems to be a bit of a glare on the photo though, but thats probably because of some bright yellow!
I think it would help to have some of the details painted in another color. Such as the lens above the lascannon barrel, and maybe some of the wires next to the cockpit.
Best of luck with your auction.