As of right now, when editing a template or a design, selecting a wall or column to edit the material just highlights the wall or column by making the selection a bit brighter, I didn’t even realise that this was a function, until I accidentally did it. Making it a bit more prompting to change the material would help introduce the mechanic to oblivious or new players.
My suggestion is that maybe we could have a line around the selection:
It’s really hard to explain in words, so I hope the picture helps.