Need ability to change the empty category unstacked/stacked icon

[RetroCro]

What will your feature request solve?

Need ability to change the empty category unstacked/stacked icon so it can be transparent like the other categories. I ended up having to copy and rename of the existing image files (copy flat-highlight and call it EmptySlot.blp) to get this look because there was no option for it in game even though I set all options to black/transparent.

Describe the solution you'd like

Describe alternatives you've considered

see above

Additional context

No response

[veechs]

An option to hide the empty slot graphics never occurred to me, but it shouldn’t be difficult to add.

[veechs]

Moved to #103.