I recall Steve Zaloga fielding this very question as he builds lots of Allied models. He said in his research he found that the majority of factory issued pioneer tools were one of three styles (in order of most seen):
1) all olive drab
2) olive drab wood, black painted metal parts
3) natural or stained wood plus black or olive drab metal parts.
But he said he prefers option 3 almost exclusively -- for artistry's sake -- to break up the monotone olive drab vehicle. Makes sense to me.