Look for your color code on the driver's side door frame. Then, go to rpm's website and look for the sharkfin antenna page. Use the pulldown menu to find you color code and the name associated with it.
I'm sure these codes are listed somewhere else, but that is how I discovered my car was not Liquid Platinum, but Titanium Gray. I was thiiiiis close to ordering my sharkfin in the wrong color when I decided I had better go out and check the code to be certain.