Converters were added in the chapter: Change is Good
Blue, Water drop = Water
Purple, Skull = Poison Water
Green, Octopus= Toxic Ooze
White, Wisp of Steam= Steam
Brown, Splatter of Mud = Mud
Some converters can be changed with the blue tap on the right with 3 lines. The type of converters it can change into depends on the level. The converter cycle will go into this order:
Water > Poison > Ooze > Mud > Steam.