Adobe Photoshop Tutorials
This tutorial will show you how to create a foam texture like this in a few easy steps.
Create a new RGB document of the size you desire.
Go to the channels tab and create a new alpha channel.
Select the Gradient Tool and set it to this:
Draw short strokes into the alpha channel until your image looks like this:
Hit CTRL-A to select the channel's content and CTRL-C to copy it.
Now, go to the layers tab and create a new layer for your foam.
Hit CTRL-V tp paste the foam into the layer.
All that's left to to is hit CTRL-U to bring up the Hue/Saturation dialogue and pick a color like this:
..and you're done!
You might want to apply some Gaussian Blur to soften the bubbles.