Hi Steve,
There are a couple of paint suppliers that make great efforts to research and duplicate original paint colors. I would start there.
http://www.nymarine.ca/
http://www.effenaco.com/
If they cannot help you then I would turn to your local paint store. Perhaps there is somewhere on your motor where the original paint color has been pretty accurately preserved; somewhere that has been protected from the sun. Bring that part into the paint store and they should be able to match it reasonably close.
Truth is…..time has faded all these colors….both in reality and in our memories. Sometimes in spite of all our efforts it remains difficult to paint them a color which we "remember" as being correct.
Chuck