(Regarding the poster version of this, MegaTokyo's fourth)
I've been poking around at ways to use coloring techniques that work with the sorta sketchy nature of my backgrounds. For this piece, the monochromatic approach worked fairly well, and i did a lot of hatching in different colors (using a multiply layer) to add more texture in the color fields. The coloring is imprecise on purpose - trying to mimic some of my sketchy approach to drawing with colorization, which isn't so easy without it looking crappy.
As always, backgrounds are an inexact science. They need to be secondary to the foreground, yet provide a place for the forground to interact with. In some ways, Piroko doesn't interact with the background quite properly (it's the nature of the original drawing) but in some ways it was a good experiment.
Oh, I now have Corel Painter installed - haven't used Painter since it was owned by Meta Creations) - and I'm looking to try some different natural media techniques with some of my colorizations... so more experiments in the future.