While I was waiting for various parts to arrive, I had a crack at making an interactive version of this. (Link)
I needed to have the cursors appear at the edge of the screen in order to not interfere with the render, which sacrifices 8 pixels at the bottom and right edges. They flicker/disappear on some screen modes sometimes but serve their purpose.
Controls are: dpad/arrow keys to move the cursor, square/Z to zoom out, x/X to zoom in on the cursor position, circle/S to reroll the colours, and triangle/A to save the render as a pcx.
Hopefully everything works okay. I'm not a programmer or a maths guy at all so I'm sure there are mistakes and the code is not very tidy but it seems to be basically functional.