Does anyone know of any Shetland ponies or Miniatures that definitely have the mushroom dilution in Australia?

It’s a pheomelanin (red) pigment dilution, and it’s recessive. It turns chestnut into a colour a bit like a cool shade of silver dapple and bay into a shade like sepia, retaining the black points.

(Photo: Wikipedia. Mushroom ponnyn Stjernens Pinja by Janny Sørensen – http://www.shetland.dk/Pocahontas%2015.html)