Finally, the diluted wash was dry enough for me to proceed, so I started adding the thermal streeting of the clouds and the inversion layer:
Unfortunately, the camera flash picked up a fair bit of reflection, but hopefully you can see enough.
This is an interesting sky required for the picture, since the actual event I am depicting took place in mid to late August. Coincidentally, that time of year was when I made my first ever solo flight, and I had been flying my ass off for the previous two days before I made that, so I well remember the skies at that time of year in Europe; it is generally sunny, but the heat kicks up a lot of thermals that turn into long streets of cumulous clouds which, if they can break through the inversion layer, always seem to have the potential to cause summer rain and occasionally thunder and lightning. With the military theme of the picture, the threatening clouds and murky inversion layer over the distant front, where the Nieuports will have to retreat to, kind of suits the mood, so I'm hoping to pull that feeling off.
It's always tempting to fiddle too much at this stage, so instead, I stopped to take a snap and make this post!
Al