Hi all,
In terms of books on Southern coaches/carriages, the standard work is: http://www.amazon.co.uk/An-Illustrated-History-Southern-Coaches/dp/0860935701/ref=sr_1_fkmr2_1?ie=UTF8&qid=1371895369&sr=8-1-fkmr2&keywords=southern+coaches+in+colour (unfortunately, it now seems to be out of print and rather expensive...)
You also cannot miss: http://www.amazon.co.uk/Southern-Coaches-Colour-Michael-Welch/dp/1906419450/ref=sr_1_1?ie=UTF8&qid=1371895369&sr=8-1&keywords=southern+coaches+in+colour (this has a couple of colour views of maroon Bulleids).
So far as is known, no Bulleid coaches made it into blue and grey, but a couple of Maunsell ambulance saloons did and lasted into the 1970s (see King for details), although colour pictures of them seem to be rather elusive.
Thanks,
Bill