i'd have the blue bricks as "background" and the dark-brown bricks as "within a wall, not walkable" bricks too. Scientifically speaking, it's more because our night vision cells are not that sensible and show everything as dark blues, so it gives the illusion that "light did not reached that area to give it colours".
Artistically speaking, blue is almost an opposite colour of brown. Thus great contrast and good readability.
And you can make your "blue bricks" appear even darker by only suggesting the bricks with their highlights (in a dark shade).
