Being an automotive painter for the last 15 years, I have seen and heard of many issues. I haven't really paid too much attention to this detail on the color differences on the fenders but now I will. Yes, plastic usually shows up slightly different than metal, but fiberglass usually doesn't. This might not be the case, but if your truck had been scraped on the fenders during shipping, a body shop that the dealer either has, or is set up with, will fix and paint your vehicle before it hits the showroom floor. If they painted the fenders, they better damn well blend the doors, otherwise, you will see the shade difference. Blending the adjacent panels will always come out 100% matching of the panels. Believe it or not, white has more variances than most colors. White doesn't match easy at all. I would have a pro examine if that's the factory paint or not. Yes you can tell the difference by looking at the orange peel under flourescent lights. I would hate to know that my brand new truck was damaged before I picked it up. God knows this happens a lot more than we think. I know cause I repair brand new dealer cars all the time due to this issue.