Early in the North African campaign, British vehicles were arriving in Egypt in their European colours. I've read anecdotes on the depots painting new lorries by lining them up, the driver staying in the vehicle with doors and windows closed. A crew would come out and coat the windows and mirrors with grease, the driver would then move forward to the paint station. They would drive forward when painting was finished and a crew would remove the grease and over spray from the glass. Wheel wells, underside and interiors were left in factory colours. Early on the rims and hubs on wheels weren't painted as the paint was corrosive on rubber. Later on the paint formula changed so they could be painted without removing the tire or masking.
Cheers,
RichB