
I would like to at least recommend adding:
Far background wall tile with text color palette + one pixel tile with same options
Background wall tile with text color palette + one pixel tile with same options
Foreground wall tile with text color palette + one pixel tile with same options
Or same tiles structure as placeholders, but with RGB color palette
So, this will allow you to choose any color from RGB palette and you can make different locations or custom objects.

Notice: This could a bit allow the game to live longer because sometimes it will be useful and players could somehow easily make new custom tiles