The picture was described as 'Greenish Grey' in a 1904 memorandum now in Boston Public Library.
Site
The Diamond Jubilee Naval Review took place at Spithead, 26 June 1897. 1
Notes:
1: 'The fleet firing royal salute on entry of Royal Yacht into the lines'; supplement to The Graphic, 3 July 1897, British Museum 1902,1011.9462, website.