So by default, when you turn it on. You can see barrier block, structure void, and light block. And the texture uses the same as when you turn on Show invisible block in a structure void. There is a small square to indicate there is an invisible block.
Image example :

Also there is a tweakRenderInvisibleBlock in the List tab too. By default the value is [minecraft:barrier, minecraft:structure_void, minecraft:light]. And player can add minecraft:air, minecraft:cave_air, minecraft:void_air to the list.

Maybe cave_air uses orange colour and void_air uses black colour instead of all the same?

nice idea