If you're doing cammo (you did say late war), I suggest a very fine-spray white undercoat to bring out the colors, and use light coats and washes to apply color. Small scale miniatures should be painted a shade or two lighter than reality, or they look like shadows from a distance of a few feet.
Layers of paint obscure details very quickly in tiny scales like 6mm, so if you can find a very fine drab green primer you like, that might be a better choice. The last time I painted any feldgrau 6mm Germans, I used as dark a mid-gray primer as I could find (not all that dark) and drybrushed them a lighter gray. The finished result looks too light up close, but okay in action on the table because the men are so small.
Testors spray paints do seem to stick to metal miniatures without primer, and in light coats dry very thin and leave the sculpted detail intact. However, they come out of the can too fast, so it's difficult to get proper coverage to hide all the metal without too thick a coat. I shudder to think of turning finely-detailed 6mm figures like GHQ into melting blobs of running paint.
I've seen some really nice primer color choices from Army Painter, but I haven't yet tried their primer, so I can't say if they're a fine enough paint.
I don't know any good ways to make cammo look right in 6mm, so I anxiously await superlative photos of your brilliant solution with bated breath. :-) A local gamer once showed me how he used a toothbrush dipped in red-brown and yellow-tan to flick a fine spatter of paint globs on his 6mm cammo German figures. That worked well enough for my weakening eyes with magnifier assistance, but the effect was totally lost on me once they were on the table.
- Ix
paints 
