Ore Base API does not support semi-transparency.

[Delocuro]

This becomes a problem when dealing with blocks such as Emerald Ore. Emerald Ore's texture has a sort of shadow effect around its ore splotches, which helps to make it more distinguishable from the surrounding Stone (as the Green in the Emerald Ore texture is almost exactly the same tone as the grey in the Stone texture). This could still be achieved by making Ore Base API support semi-opaque pixels in ore overlay textures, but since it does not currently, ores such as Emerald Ore look very odd and hard to see in caves.