As you can see in the picture above, I've finished painting in the various other elements of the figure. I've painted a dark green over all the black elements I want to be green and I've painted the base Boltgun Metal, followed by a wash of Devlan Mud.
I don't know about the rest of you (because my network of spies isn't that efficient), but I really do have to be disciplined about thinking about the entirity of the composition as I'm painting, rather than focus on a bit of detail at a time. This was something my A Level art teacher used to berate me for and quite rightly too. If you don't work on a piece in its entirity, what you end up with is something that looks oddly inconsistent. But, it is soo easy to get drawn into working on the detail of particular aspect of a model up until its finished, then move onto the next part. You can create a consistent effect that way, but it is much harder and the risks of getting it wrong are a miniature that looks, at best, weird and at worst like it was painted by a few different people on different days.
The airbrushing really helps with this, because I can quickly do the early stages of the core colour scheme over a number of figures quickly and consistently. After that, it is just a case of picking which element to paint next and doing that for all the figures. Honestly, I find this can be a bit tedious at times, but I also find it the only way to create a reasonably consistent finish.
This is probably less of an issue if you're painting just a single miniature, but even then I'd still strongly advise in trying to paint all aspects of the model in stages, rather than finish one bit and move onto another. This is because getting other elements painted does change the contrast with the other paints, which in turn can parts already finished now look odd.
As I mentioned earlier, all the green bits were first painted black. I've previously tried to avoid this step as a time saving measure and, to be blunt, it doesn't work. It doesn't save time. On a miniature as lightly coloured as this, you'll have to apply multiple coats of green paint to even get the colour somewhere approaching the dark shade needed. Painting black is an additional step, but it saves time in the long run. Don't skip it.
I also want to talk a little about the paints I'm using. Above is a picture of the Bone Triad from Reaper Master Series, with paints sorted darkest to lightest (left to right). Apologies it is not so easy to see the different tones, I accidentally spray painted the Aged Bone bottle.
By now it should be clear that I'm a fan of Reaper paints. They have great consistency, water down well so the pigment doesn't separate and the little dropper bottles are much better for keeping the paint fresh. Okay, occasionally you need a pin or something to unblock the nozzle, but that is preferable to me than having to rehydrate an entire bottle of paint. Something I have to do with the citadel paints, frequently.
The other great thing about the Reaper Master series is that the Triads have been really well thought through. The different tones work together really well and indeed, you can apply them sequentially without the need for much blending. I know citadel and other brands have all got on board the bandwagon of organising paints into triads of dark, mid and light tones, but they don't do it nearly so well as Reaper.