I read on a thread today, from @jhb171achillI think
Up to 1903: all locomotives, goods included - a shade of green barely darker than current Isle of Man, or not unlike the LNER in England. Frames brown, lined red, green parts of loco lined in black and white. On tenders, "M G \\ W R" (\\ denoting the MGWR crest). Lettering shaded gold.