Evidently, as with most railroads, the color depends on era and paint scheme. Pick an era and and lettering scheme, then paint it the color that matches that scheme.
Dave H. Painted side goes up. My website : wnbranch.com
here is one group that might be a good resource
https://www.anthraciterailroads.org/
Ron High
Photos of models from https://www.pwrs.ca/announcements/view.php?ID=5350
It appears it depends. Image searches shows various shades
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
What color were Lackawanna cabooses? It almost looks more brown than red.