I wouldn't go so far as saying F&M's have bad paint by any means, but some of the lighter metallic cars will show a slightly darker bumper under overcast or artificial lighting. Both Maserati and Ferrari have gotten far better in the last few years (look at a Fly Yellow 348 Ferrari, and you'll likely see three different shades) It's not something most people notice, and as soon as you get these same cars in the sun and you would never see a difference.
That said, yours does seem a bit more of a difference than what I have seen in the past, but its hard to say without seeing it in the different lighting conditions..