Diffraction "rainbows"

At the church I attend there are some window decorations that are essentially diffraction gratings oriented in a variety of different directions.  When the morning sun shines through the gratings, an arc of colored lines appear on the opposite wall (top).  Now real rainbows (bottom) are a refraction phenomenon, not diffraction, but the resulting color pattern is the same, plus it is a good illustration of the impact of wavelength on diffraction patterns.