First, great find! Usually, I'm more for the "turreted MG" branch of armoured cars (easier to integrate into infantry-focused games), but that one is quite nice.
Second, all the pics I've seen have the crew's tunics/jackets darker than the colour of the vehicle's hull. I'd say Navy blue uniforms wouldn't be too much of a stretch, especially when operating as an "expeditionary corps", e.g. early WW1 in the West.