we painted one of our glass doors with paint.
I got the idea from the ever-creative Sara Mincy, who always shares her colorful and fun family friendly activities. Like Sara, we just used the cheap $1 acrylic paint bottles. (It comes off very easily when your ready to wash it off)
I used black and quickly painted in the lines of the designs. It acted as a "coloring page" of sorts, so the kids had a clear guideline of what to paint.