May I suggest another hyothesis?
The Light Blue paint, Dark green, Black and Red, were classical paints for metal parts and machinery (locomotives, heavy engines and such) in Europe from the thirties to the mid-fifties, widely available. the Soviet for instance used quite regularly locomotive paints on their bombs, as they seem to always have had problems of availability of regulation paints.
The issue of camouflage of bombs under the fuselage of a bomber is much less relevant that the camouflage of these bombs on ground stakes, which benefit from dark colors (dark green/ grey-black) in Europe, except during the snowy winter months, when light blue would be a very good alternative to white, which anyway was more available as wash rather than a real metal paint.
Photo evidence shows that it was a regular policy in the RAF from 1940 onwards to spray the the bomb sacks in dark green, to camouflage them, leaving the bombs half yellow half green.
The US Navy initiated from the beginning of the war in the Pacific, an unoffical spraying of the bombs (Yellow, which was the colour of high explosive bombs in the US, UK, France, Nederlands etc.. in the thirties) with what was available on board the ship for camouflage repairs - navy light grey, a practice that became official only in late 1943.
The Beige-Grey paint would obviously have fulfiled the same aim for the Germans in North Africa, while less easily available.
I do think that regulations on such matters often conflicted with the reality of the war such as availability of supplies and deployment of air units to widely distant areas with different weather conditions.