Gradients, Layers, Transparencies. How is this done?

[onesquareinch]

hello everyone,
can someone explain how this image is done? i've tried using opacity levels, but the color doesn't look as vibrant.

 

[Gaussian]

Welcome.

Make 3 circles of the same color (use eye dropper tool), place the middle one on top and adjust its blending mode and opacity in the layer palette (experiment). When done throw them all into a group, duplicate this group 2 times by dragging/dropping the group on the new layer icon at the bottom of your layers palette and change the opacity of these 2 new groups accordingly.