Gimp generated "paper marbling"

[Ofnuts]

Off the cuff attempts:

• Fill a layer with Filters>Render>Noise>Solid noise
  
• Apply a wavy curve on each color channel (different color curve per channel)
  

   

   

• Repeat the process with another layer, press New Seed in the dialog to ensure you generate a different patttern
  
• Experiment with layer modes on the top layer, here with Darken Only