Step 1. Render Difference Clouds

Fill a layer with black and go to Filter » Render » Difference Clouds. Repeat (CTRL/⌘ + F) until it looks nice to you.

Tiles: Difference Clouds

Step 2. Create the Tiles

Duplicate the layer by draggin the layer onto the new icon in the layers palette. Then go to Filter » Pixelate » Mosaic. Play with the number until you get nice-sized tiles.

Tiles: Mosaic Selection

Then go to Filter » Sharpen » Sharpen. Repeat (CTRL/⌘ + F) two or three times until you get nice sharp edges.

Tiles: Sharp Edges

Set the layer to "Screen (or "Overlay" or whatever you want, really) and play around with the hue/saturation.

Tiles: Screen

Or keep the layer opaque:

Tiles: Opaque