This is a single day activity designed for classes familiar with using Adobe Photoshop. It would work well with a Substitute Teacher if the students have used the program before.
The idea is that students select a Zentangle / Zendoodle Design and use Adobe Photoshop to fill the spaces with color. They use the paint brush tool, paint bucket, gradient tool, and filters to fill the spaces.
This was created using Adobe Photoshop CS4, but should be similar to other versions.