This looks good based on the screenshots, but I can't get it to work. For some reason, I only get a black screen after loading. 
Oof, this is a difficult one to debug!
I think it's an issue with how I'm preparing the surfaces for use with the palette swapping shader.
I've just posted another updated version with an attempted fix, let me know if this loads for you now and thank you kindly for all your help identifying these issues <3
