Bygone-focals: glasses that allow you to see the original terrain

Bygone-focals are a tool that is placed in the head armor slot to allow you to see the natural world generation in place of player-placed blocks or otherwise modified terrain.

The original blocks will be outlined in green and places where blocks exist where no blocks were before will be outlined in red, in a similar effect to the glowing effect caused by spectral arrows. These outlines can be turned off by hitting F1. You cannot collide with these blocks.

You can craft bygone-focals by putting two ender pearls in a workbench horizontally and a stick between them.

The uses are being able to restore terrain accurately to the original world generation, and taking before/after shots if you forgot before starting a build.