In the left illustration, I'm using a technique that I've been using a lot at work lately in doing quick concept artwork.
I sketch the full image out in pencil and then lay some digital watercolors underneath it in additional layers.
It's only barely visible here, but I've gone in and recolored the pencil lines so that they are in a warm brown
for the foreground characters but are a cool blue for the background.
The whole top half of the image is pretty simple because it was obscured by the title logo.
On the right, I've taken the same line drawing, run it through a color copier
onto some Strathmore Bristol watercolor paper (thus bonding the lines to the paper)
and watercolored over the whole thing. It's not as dark an image, but not without a certain mood.