That's a blend mode, accessible from the layers window. The layer you want to change needs to be above the layer you are blending it with. Then click the drop-down box that currently says "Normal" and change it to "multiply." You should see the clouds layer reappear with the black areas of your original shape superimposed on it.
Honestly, I haven't been able to get this technique to work in Photoshop, either, but this is the first I've seen m5pig's translation.
For the sake of further reading, here's a tutorial about the different blend modes and what exactly each one does: http://www.cgtextures.com/content.ph...ame=blendmodes