final-result

Create this awesome rainbow effect on your landscape-photography master pieces.

This tutorial is from http://www.photoshopessentials.com/photo-effects/rainbow/

If you follow alongside the tutorial, then you could probably grab their sample image, but if you are going to attempt one of your own images, be sure to choose one (or if you know your stuff, correct one) to the point where it fits the mood of the rainbow effect you are after. Rainbows such as this one, usually happen on overcast days when there is a little sun peeping through, be sure your initial image reflects this quality for maximum results.