Open a new layer above the sky's layer. Then select the Elliptical Marquee Tool and press the shift button to create a round marking. Paint it out with the necessary color.

Fantastic Sunset Wallpapers

Insert the same way several more circles:

Fantastic Sunset Wallpapers

Then we have to outline the elements, choosing previously the next option: Layer – Layer Style – Stroke.

Fantastic Sunset Wallpapers
 


Create a new layer above the circles' layer and group out both layers: Layer – Create Clipping Mask (ctrl+g). The Gradient Tool will be helpful in decolorizing several of the circles.

Fantastic Sunset Wallpapers

Merge down the layers: Layer – Merge Down (ctrl+e). On a new layer we have to represent one more set of the circles, changing a little the colors and moving the center. Place this layer lower than the big circle's layer:

Fantastic Sunset Wallpapers