It really depends upon date and theatre, predominantly trucks were in the light olive green, Vallejo have a IJN vehicle paint pack
light olive green – Model Master 2051 faded olive drab/ Val 73611
dark green – Model Master 2114 Imperial Japanese Army green/ Val 71134
tan, tinted with yellow – Model Master 2053 sand + yellow /Val
dark brown- Testors 1183 rubber
yellow – Model Master 2118 deep yellow
Prior to 1943 the official camouflage scheme was:
A single base color of light olive green.
OR
This camouflage pattern:
light olive green – (base color of 50% of the vehicle)
dark brown – (30% of the vehicle)
tan – (20% of the vehicle)
yellow – (stripes or bands)
After 1942 (the start of the Pacific War) the official camouflage scheme
was:
dark green – (base color of 50% of the vehicle)
dark brown – (30% of the vehicle)
tan – (20% of the vehicle)
yellow – stripes or bands were deleted
light olive green – After 1942 an order to paint the underside of the
barrel
and the lower chassis below the fenders in this color was issued.
In all other areas after 1942 (China, Manchuria etc.) the official color
scheme was:
light olive green – (base color of 50% of the vehicle)
dark brown – (30% of the vehicle)
tan – (20% of the vehicle)
Hope that helps
assembles and paints 
