Durkota, et al., show three Muromets in "The
Imperial Russian Air Service", Flying Machines Press. Two of these are a sandy brown color, somewhat darker than CDL. However, the text says that almost all of them were finished with varnished linen. The third Muroments, a model G3, is a light grey in color. It is listed as being the only Muromets in this color.
What do you think of the models? I recently bought the Muromets myself and was impressed with it though I'll probably never assemble it.