In this image, it's not that hard to distinguish the background from the normal tiles. In-game, this would most likely be different. I don't know if it's just me though.
I agree.
I think that background/foreground and normal tiles should be different but similar, if that makes sense
like you look at the whole thing and see that all the layers mesh together but still being able to distinguish them
or something
like in the image the background is darker and has brick tiles but the grey blocks are still very similar to the normal ones