I did the cover by hand with pen and ink, scanning and converting my drawings to vector art and then coloring them digitally. For all the digital work, I used Inkscape.
The colors stand out on tablets quite nicely.
I also did the 50+ interior illustrations and wrote half the book. I'll be posting more about the art in the coming weeks.
The early release PDF is now available here: http://twoscoopspress.org/products/two-scoops-of-django-1-8