Well, I've finished the outdoor background. I wanted it to have a coloring book kind of look to it and I think I succeeded. You notice that I made some minor alterations to the hills in the picture. I thought this change and the dark outlining for a few of the elements would help to give the picture more depth without making it too complicated.
I painted it with high gloss, Rustoleum, water base paints. Their selection of colors is limited but by mixing them together I was able to get basically any color I wanted. All in all I very happy with the result.