Hello James,
That picture comes from here:
http://www.mapleleafup.net/vehicles/softskin/15cwt.html. Reportedly, it is an original canvas cover but I cannot confirm the original colour. It could well be faded khaki/green, as I think it is too dark for sand. Canvas came in sand, khaki and brown, depending on the colour of the truck - see
http://www.mapleleafup.nl/cmpvehicles/paint.html.
Pre- or early war vehicles seem to have (also) been fitted with sand coloured canvas, as demonstrated by the extremely comprehensively restored Morris-Commercial CS8 15-cwt truck from 1936/1936:
http://www.milweb.net/webvert/a2712/91520. You could ask the owner, Rory Ballard, for more info.
In general, when war broke out, lots of effort was put in proper camouflage. So pre-war gloss painted vehicles with sand canvas were quickly painted in appropriate camouflage to blend in with the surroundings where the vehicles were used - see
http://www.mafva.net/other%20pages/starmer%20camo.htm.
HTH,
Hanno
