This is a technique to create dark clouds with light shining through the cracks. It creates a neat effect if combined with photo images.
Create a document and go to FILTER>>RENDER>>DIFFERENCE CLOUDS.
Press CTRL+I to invert the colors.
Go to IMAGE>>ADJUSTMENTS>>LEVELS.
Make a new layer and fill it with a color. Change the blending mode to "Color". Your clouds should now be the color of this layer.
Final Result