Rainbow Maker is a graphics editing tool for the Mac. It can be used to add a rainbow effect to your pictures. There are different rainbow effects that you can add, the default one is the primary rainbow. Other available effects are primary and secondary rainbows, rainbow 22 degrees halo, rainbow 22 degrees and 46 degrees halo, glowing clouds and brocken spectre.
To test the application, I loaded an image by clicking on the "Open" button. Unfortunately, you can't drag and drop, which would make loading images easier. Once the image is loaded, you can "make" the effect. If you didn't touch the settings before processing the image, you will see a rainbow at the top of the screen. You can move it around the image with the position controls on the pane on the right. If you want to reset the effect's position, you can click on "Initial". Some of the effect options that you can change, other than relative position, are radius, saturation, brightness, alpha, and displaying the dark. The effects look good enough if you tweak the settings a bit. Perhaps the only negative comment I can make about this app is that you can't edit the image at all. In one of the images that I loaded, the effect would have looked great if I was able to rotate the image, but I couldn't do that from within the app.