Hi Guys:
So far as I can tell, Mauretania's funnel bases were painted brown as were the deckhouse skylights on the top of house. I don't think this changed thoughout her career. Of course, black and white photography has limitations so far as colour interpretation goes, but it would seem that the shades of grey around the funnel bases matches the "grey" of the deckhouses. I have consulted the various books I have on the subject and haven't noticed any variation.
I know that the Gunze version of the Lusitania has the funnel tops braced by two bars across the top as opposed to Titanic's three. It is likely Mauretania had a similar configuration, but I cannot say with any certainty. I can check the funnel rigging for you: I have the Shipbuilder reprint of the Cunard QSTS Mauretania from 1907.
Cheers,
Mike M.