A decorative paint finish is a good way to customize an interior in only a short time. Use a latex glaze mixed to the color of your choice. Dip a natural sponge into the paint mixture and apply firmly to the wall. Drag down the wall, creating the design you want. Always work top to bottom and in one direction. Latex paint will dry within an hour, and you can apply an over-glaze for a beautiful satin finish.
For more on painting, consider:
How To: Rag Paint
DIY Wall Stenciling
10 Reasons to Go Crazy for Chalkboard Paint