How to create rainbow using PSE?

1. Open an image in PSE Editor. Create a new blank layer by clicking new layer icon in layers palette.

2. Click on the Gradient tool from the tools bar.

3. From top bar select the Gradient picker dropdown.

4. Select Transparent rainbow as the gradient type(second last in the list).

5. Now select the Radial gradient form from next to this dropdown list. (Marked as no: 5 in the screenshot). Now draw a line in the image where you want the rainbow. And using Move tool,  move it towards the edges such that only a semi circular region is shown.

6. Now keeping the same new layer active in the layers palette, reduce the Opacity of the layer to give it a transparent rainbow effect.

Here are my initial and final images:

I hope you find it easy and useful !