Revell of Germany have Gelb-Olive (yellowish olive) in their range. It's number 32142 from the enamel range and 36142 from the Aqua range (acrylics).
I suppose you could also mix up your own using some shade of olive green with a bit of yellow thrown in.
I picked up a 'cube' of Aqua 36142 from the LHS, broke our the Iwata & found a bottle of Vallejo Air 71013 Yellow Olive....
So a quick comparison with the Revel Aqua 36142 Yellowish Olive was in order.
Vallejo as usual sprays well, but I use their gloopy thinners, & the colour was, to my late night eye, a darker blue-greenish.
The Revel Aqua, comes in a self-sealing rip-the-top-off & use as a paint pallete lid, was fairly thick, & in my haste, I probably didn't stir well. Nontheless, I used the Vallejo thinner & sprayed away.
The colour was a bit faded-olive drab.
My Experiments here:
http://www.militarymodelling.com/albums/member_album.asp?a=8133V 71043 Olive Drab on Sherman for comparison.
V 71013 Olive-Green & Revell Aqua 36142 Yellowish Olive on bridge
I rather like the V 71013 Olive-Green for '70's -'90's German kit, though...