As an experiment, I've been trying to do this. At first I tried the various tutorials from around the web, but the result doesn't have the realism of real rainbows such as variation of color throughout the bow, the small rain droplets especially underneath the bow, and the various shades below and above the bow. Also, most bows have some sort of repeating pattern of one of the colors underneath of the bow, most often white, and most prominent toward the bow's center. I've tried repeatedly to make it as realistic as possible, but the result is always too flat or lacks color. I've had somewhat more success with partial bows for some reason, but when it comes to the entire bow as I desire, no. Have there been any tutorials written that address these issues and/or any suggestions would be welcome. I also did try modifying the rainbow gradients and this helps a bit but there has to be more than that.