The Diagram allows different piece types to use the same image. Even the same ID. And it is smart enough that when this ID is in the promoChoice, it would not allow promotion to the type that would itself morph to something else on that square. In the Elk Chess Diagram I did use different images, though. (Flush your browser cache if you want to try this, as it was a recent patch.) As a player I like that better than having to pay attention to square shade.
Other examples of Diagrams for variants with position-dependent moving:
The Diagram allows different piece types to use the same image. Even the same ID. And it is smart enough that when this ID is in the promoChoice, it would not allow promotion to the type that would itself morph to something else on that square. In the Elk Chess Diagram I did use different images, though. (Flush your browser cache if you want to try this, as it was a recent patch.) As a player I like that better than having to pay attention to square shade.
Other examples of Diagrams for variants with position-dependent moving:
https://www.chessvariants.com/large.dir/contest/bigouter.html
https://www.chessvariants.com/usualeq.dir/amalgamated.html
https://www.chessvariants.com/rules/crouching-stepper-hidden-rider