I did a quick study to figure out which colors I wanted to use. I used Winsor and Newton pan watercolors and watercolor markers, Faber-Castell brushpens, and Copic, Prismacolour and Mexpy markers on Canson Universal Sketch paper, which isn't really meant for wet media but I love how it looks on it nonetheless.
I did the sky first, to set the palette for whole thing.
Partially colored, with just some of the markers I used. They like to fall off the drafting table.
Now coloring is finished; I just have to touch-up ink the lineart. You can see the lack of outline definition especially on Apen's (the dark-haired fellow) face.
And a digital photo of the finished painting. For posting I use a scan, not a photo, because the resolution is better, but each version captures some of the colors that the other doesn't.