Have you ever seen a beautiful rainbow and thought, wish I had brought my camera? Well if all else fails you can always add one with photoshop. There are several ways to do this but this is my version, which I have simplified as much as possible.
Open your image and make a new layer like so.
Next select the Gradient Tool in blue. Go to drop down, click on little arrow top right of box and select special effects. Then click append.
Select box (blue arrow) and click on radial gradient (blue circle).
Now let's create the Rainbow.
Place the cross hairs to the right of the image and hold and drag to the left of the image. Once you release your rainbow is formed. Like so! (REMEMBER You can drag from left to right or top to bottom depends on the shape of rainbow you require.)
Now go to the layers bottom right and change to screen and drop the opacity (marked blue). I dropped the opacity to 22 % to create a subtle effect.
Now go to filter- blur- gaussian blur. Set a radius of around 50% and select ok.
You should end up with a nice rainbow.
Because I have water in this image I wanted to keep the reflection but remove the rainbow on the bushes. To do this is simple, just select the History Brush and paint over the areas where you want to remove the rainbow colour.
Finally go to layer on top tool bar and flatten image.
There you have it, a nice Rainbow effect.
As always if you have any problems let me know.