Good technical work! I would have coloured in golden the little triangles that remain white near the center of the axis.

In this tutorial, step 11, is a quick and dirty way to make a brush to paint clouds. It's not a rasterized "cloud brush" so to speak. It uses brush settings to "paint" clouds. There are other advanced and more tedious methods, but this takes just a few minutes to set up the brush and you have it saved forever. You can use different layers while painting and maybe make these layers darker or lighter to create depth.

http://www.pxleyes.com/guide/57122/the-making-of-Clown-in-a-Car.html