I have a 52 66 RC Diesel WF that I use for making hay.  I put lights on it a couple of years ago and had the same question.  

From what I could tell the early tractors had the black painted lights while later ones had green.  I'm guessing that change could have occurred in 52 when they changed shades of green, but I don't know.  

If you look on the cover of &quot;Oliver Tractors Photo Archive&quot; by P.A. Letourneau there is an original photo of a  77 Diesel, the lights are painted green.

Jon