[DustyPorViva]

The black is very, very noticeable.
Maybe your monitor is the one not set to normal(100[percent] brightness and contrast is the recommended settings. Though I still keep my LCD set to 75[percent], because it's too bright otherwise, and it's still very noticeable).

I've attached an image...
Red is the correct tile for caves... though it's blocking(I guess that doesn't matter, as you were using blocking tiles anyways).
Yellow is what I prefer to use, noticeable, but not as much. I only use it because it's walkable.