You can go to a body shop and they can either find the matching paint, or mix it for you, heck, they can even paint that piece for you. I don't know about metallic blue, little to loud for me, black is always nice, but it's your car.
take a picture of the trunk piece and use image editing software such as photoshop to change the colors around, that way you'll see how your car will look with the piece in different colors without actually painting it.sicksilver99 said:black might look good but im afraid another color would look like i got that piece from the junk yard