I have the same locomotive. It has been the most reliable locomotive on my railroad. I run it with the 20-6576 set. The cars are much darker than the locomotive. Hard to know whether the locomotive is too light or the cars too dark or, maybe, both. The 20-65236 set appears to be lighter than what I have. They may be a closer match.
Color pictures of the prototype seem to be a medium to light gray but 70 year old color photos are suspect.
Maybe someone else has a better answer for you.