Then I was a bit unhappy with the shading under the figures. So I added a bit more background with watercolor. And then some more. And by that time, it was a big amorphous blob background, so I needed to tighten everything up with acrylic paint. And then I started just painting with orange paint to see what would happen...
Anyway, this is the end result. I really like the richness of it, compared with solely using watercolor. Back in art school, I was more of a stickler for staying within the medium. However, one of my professors told me that when you're an illustrator, you use whatever it takes to get the picture finished. If that means throwing oil paint and crayons on a pen and ink drawing, then so be it.
This also shows how much fun it is to do a project that's basically mine. If this were a series for a book, changing media at this point would probably give the publishers conniptions. The best I could hope for would be a "Very nice. Now do one in watercolor like all the others." But these are not only books for my kids, they're a way to grow as an artist through practice, so it's fun to push these things in a different direction.
On a side note, T is for "Take the stairs!" said the platypus. The reason for the shocked look on Arianna's face is the number of stairs they have to take (for the rough sketch of the stairway, see my older post: http://art-sam-ples.blogspot.com/2009/06/ariannas-alphabet-book-rough-sketches.html).