On a lark I decided to do a lil bit a both.
I bought some of those Windsor Newton water soluble oils -- I picked up their olive green and also some ochre as well as a yellowish color. Also some of the thinner stuff they make for their water soluble oils -- you can clean up with water, but thinning is I think best done with their stuff.
I think I'll lighten up the olive a bit with ochre and maybe some of the yellow and see how it works as a drybrush. Got a nice #2 round brush as well. Well, I'll see the results soon enough -- and so will you! I'll post pics of the Mack and howitzer when I am done drybrushing.