See how you CAN se though some parts of them? Overlay IS working.

But if you look CLOSELY at the textures with your image editing program,
you will find the black area that is still showing isnt REAL black.
It is shades that LOOK black to the naked eye, but are slightly above black.

If the red OR green OR blue component of the color is 8(out of 255) or higher,
you will still be able to see the pixel, because overlay will not hide it.