Here's one explanation has to how I might approach the background imagery.
Here's my original.
Then I apply a threshold filter.
Clean up both the black and white areas using the Brush Tool.
Then use Color Range (or other tool of choice) to remove white BG.
All that's left to do is add a BG color.
Then I can use a solid color adjustment layer clipped to the black copter layer to make it any color I wish.
You can add more clipped solid color layers in different colors or you can just adjust the first one to change colors.
As for the soldier, he could be a threshhold, cutout, or posterize filter with some added effects. I haven't played with that effect yet.