In this tutorial, you'll take the picture from this to this:

Open the picture you want to work with. If you want it icon sized, it should be 100 by 100 pixels. :]
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Make a new layer and fill it with color 33CC33. Change the blending mode to Lighten. Make the opacity set to 70%.

Make a new layer and fill it with color 333399. Change the blending mode to Screen.

Make a new layer on top of everything and choose a large, soft brush. Change your color to white and click once in the upper right corner so there's a single white spot, with most of it off the edge of the canvas. Change the blending mode to Overlay and set the opacity to 50%.
Make a new layer and make a new white spot in the same corner over the other spot (which you probably can't see that well because it's on Overlay). Change the blending mode to Soft Light.

At this point, all you need to do is finesse it a bit more and maybe add some tiny text. :]

And ta da- you're done!