Basically right Joe.
I generally mix my oils on a white ceramic wall tile. That way I can vary my mix from very thin, right back to the original paint.
For the grass I tend to work from thin, and increase the paint until I start to lose the pesky non-greens. If the paint gets too thick, a drop of turps on the brush soon sorts things out. My first intent is to get the deeper bits of grass as dark as possible. Once the initial application is dry, I move on to the lighter shades which I apply without thinning, with minimal paint on the brush, as a mix of gentle stabbing and dry brushing. Experimentation should give you a feel for what's best.
For the armour, I tend to use Van Dyke Brown (other colours can be just as good), again with varying thinning. I'll try a thin pin-wash first. If that works, then fine. If not, then I move up the thickness until I get what I want. Any excess paint can easily be removed with a clean and nearly dry brush.
Hope that helps.
Cheers,
Andrew
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