I would have though that the 'chants' were built using available parts, that would include any canvas materials?
I know i stated that canvas come in several colours, but know that greens and greys are the typical however the Komet i'm working on original has a yellowish canvas covers for the life boats, (as this matched the funnels colour)
I guess that colours of parts can only really be sort through looking at documents or asking those who were on them or built them, as black and white photo' are very deceiving when telling colours, light shades indicate a light colour,(cream, white, grey, some greens in the lighter spectrum) dark shades or black indicate just dark colours ( from black through to browns even reds and some blues) so its very hard to tell what is right?
Personally i would be happy with the brown i think they look the part on that model, but if your not happy...then its your prerogative to change them, after all you have to live with the model!