Hi, your question is just in the right forum. That batwing is late-49 to -54 only. The problem is that I have not found any source for the correct colour either. The same colour is also used on the steeringcolumn gearshift stick and seatframes....
I sure hope that someone would come up with info on that colourcode. My collegue "Doodah" just put up the same Q on TheSamba forums...