Automotive touch up paints work pretty well, but tend to fade out quicker if left out in the sunlight much. That can be somewhat delayed by spraying over it with a good UV protectant clear coat.
However, since you are doing a part that is not going to be in the sun much you should be ok. I would clear coat it anyways though for some added protection.
P.S. Dupli-Color works pretty good and may be cheaper?