From Looney Pyramid Games Wiki

Opaque Pyramids[edit | edit source]

This category includes those games that require opaque pyramids (be they grey, white, or black). It does not include those games that merely suggest or mention opaque pieces or where the opaqueness of the pieces are inconsequential to play (where colors are interchangeable and opacity irrelevant). Games that use an opaque to either hide information or to make it easier to identify a player's ownership of a stack (an opaque used as a solid base under any number of transparent pieces) qualify for this category. Thus games like Volcano aren't included, as volcano caps can consist of any unused color without altering game experience.