I would actually just put this as a lens that can be toggled and that activates on city build menu or just the city menu. Most of the game, you dont need to see this especially because once the decision is made, it's made. A culture district tile will probably always be a culture district tile because overbuilding is just rebuilding the same kind of building on the same tile. Placing a population growth this is irrelevant because it is more about watching yields. Placing buildings is really the only place this could be useful but even then it is minor because you are looking more at mountains, resources, and coast.
Plus, this criticism is invalidated, from my perspective, by my own criticism that overbuilding is a repetative unfun mechanic that makes building new buildings feel monotonous and superfluous. This isn't really needed outside of the build menu due to how adjacencies work in 7 and would only take away from the current look of the game IMO (which looks fantastic) for no real benefit. I dont need to see purple on the main map where my obelisk is and blue where my library is. As it gives me no information that is useful in this system.