The Acid Dye is a dye that causes a rippling black and green effect on your armor or anything equipped in the social slot. Acid Dye is obtained from the Dye Trader randomly after offering him a Strange Plant.
The Acid Dye will behave strangely on the Crimson Heart light pet, often distorting the rippling patterns.
It also does odd things if applied to Grappling Devices. This is useful though as it makes the lines visible in darkness even if they don't glow.