Most rooms have subtle shadow effects cast over them from above - planks of wood in the Basement, bars in the Depths, veins in the Womb, etc. This mod makes them darker and a bit more obvious to add to the atmosphere.

To install, extract the context into the resources folder. Also includes a fix for the overlays in Sheol (they appear in the Dark Room instead because of a typo). If you don't want this, don't extract fxlayers.xml

EDIT: This works with Afterbirth if you don't extract fxlayers.xml, though the game now has bug in the overlay system, which means not all the rooms will show the shadows.