1970 300 convertible. I am replacing door panels purchased from SMS. The armrests in the back seat are separate from the rear door panels. A single piece of molded plastic I presume. They have yellowed somewhat and will not match the new door panels. I expect that unless I can find NOS, not likely, then the next alternative will be to paint the originals to match as closely as I can. I welcome advice on how to do this. What kind of paint?