First press d on the keyboard to change your colours to black and white, then go to filter> render> clouds. Then go to image> adjust> threshold. Use the default settings and click okay.
Step 2: Colour!
Now use the magic wand tool (below the move tool) and select all the black, or white. Make a new layer, then fill your selection with any colour you want. Then make another layer beneath it and colour it all in any colour.
Step 3: Lather, rinse and repeat.
Keep and doing this with different colours 'till you get the look you want.