tile squares with random colours from a palette

[Ofnuts]

• Generate solid noise (defatil roughly the size of the tiles) and add contrast
  
• Filter>Blur>Pixelize by the size of the tiles
  
• Copy to channel
  
• Add you color layers
  
• For each color layer (except bottom),
  • add a layer mask and initialize it to the saved channel
    
  • Threshold the layer mask (high values on top layers)
    

With some luck some of it can be done with my luminosity-tiler script.