We approached this as an expressive self portrait of the artist, using one of our most important art-making tools for inspiration - our hands. Students were asked to create a composition by tracing their hands, and building the design from there. I told them they could not add other elements like stars, hearts, people, etc. The students and I reviewed various color families that we learned about this year - primary, secondary, complementary, analogous, warm, cool, neutral, etc. Students could choose any colors they wanted, but I encouraged them to think about the different color groups to help them limit their color palette a bit. It can be tempting to just use all the colors in a project like this (not that there's anything wrong with that - that, of course, was a choice too!) I wanted to make sure that students were being really conscious of their color choices.
This project is really easy and simple and incredibly effective. It can be done in 30 minutes if necessary - though a slightly longer class period is preferable for more detailed designs. I have three trays set up in the middle of the room: one for washable markers, one for permanent markers, and one for crayons. For this project I got twistable crayons, and they have been AWESOME. They come in a great variety of colors, have lasted through many, many classes and allow the students more control when drawing.
At the end of class, each filter was placed on a couple sheets torn out of the phone book and sprayed lightly with a spray bottle. Less is more here - too much water will wash away too much of the washable marker. A light spritzing is plenty. The phone book pages help absorb the extra water and keep the filters flat while on the drying rack.