Darkness stirs on the rim. Survive flesh infestations, cultist attacks, shambling undead, blood rains, invisible hunters, and other sanity-shredding perils. Capture and study entities to harness the power of the void. Conduct psychic rituals and awaken an evil machine god.
When you arrange them in order of release, they spell out "R.O.Y.G.B.I.V," which is an acronym for the colors of the rainbow: Red, Orange, Yellow, Green, Blue, Indigo, Violet. This was a deliberate choice by the developers to create a mnemonic device to remember the order of the colors in a rainbow. Here's the breakdown: