The M151A2 is a pretty decent kit, except that the rear end sits too low, but it still builds up nicely. Do you have the original Tamiya or the Academy copy? Operationally, the M151A2s were normally painted in the US Army four color MERDC scheme. The four colors used were based on the area where the vehicle is located. Normally a woodland/temperate scheme was standard. The base color of this vehicle was forest green, the secondary color was red brown and there were small squiggles of tan and black "sea gull" shaped "V"s applied. Seats were a very faded OD green.
On earlier vehicles, the wheels were painted green and red brown (alternating). Later vehicle wheels were just painted flat black.
In a desert location, replace the green with sand (more yellow than the tan), jungle location replace the red brown with a light green.