Hi Walter,
Working from memory here. After her first three trips as a transport in a dusky or dark scheme, the Mauretania was laid up until September 1915 when she underwent conversion to a Red Cross hospital ship with white hull, green stripe, red crosses, buff or "yellow" funnels (it has been noted some Cunard vessels may have retained Cunard orange funnel colors) and (possibly) an illuminated sign or crosses for night identification. She made three trips from Southampton to Moudros in October, November and December. She was released in late January 1916 and dismantled as a Hospital ship. When called again in September 1916 she was again painted into a dusky drab scheme for her voyages between Liverpool and Halifax. She would not wear any dazzle scheme until early 1918. Hope this helps.
Best wishes,
Eric