On the subject of paint, it would seem that these CMP trucks came off the line painted OD or OD/Brown. They were then field painted for North Africa in the colours of the day (which I was surprised to learn varied a lot in the 'specs' from the War Office - sometimes changing twice in a year.

As this one was 'acquired' by the Italian Royal Army (RE), I'm thinking of priming in OD, then an appropriate British desert colour (with a 'u'), then add Italian field painted camo bits.

The desert campaign offers a lot of latitude, what with the differing climates, weathering and terrains across North Africa, field painting and camo, improvised and regulation schemes. And because the two sides overran each other on several occasions, each had access to stores (including paint) left behind.

Edit: replaced OG with OD as per Jakko, below, d'uh!