Rainbow Dust is a powder that is first seen in The Faceless Ones. It is used to detect traces of magic that have recently been used in the area. To use it, the powder is sprinkled in the air, and will change colour to indicate whether magic has been used, the specific colour the powder turns indicates the type of magic present. It also gives an indication of how recently the magic was used, possibly through the vibrancy of its colour.
Skulduggery uses Rainbow Dust again to investigate the death of Bernadette Maguire. This time it detects traces of Adept magic, and that it was used in the last ten minutes Skulduggery, Valkyrie and Fletcher arrived at the house. The magic used was Necromancy, and Bernadette was killed by Bison Dragonclaw.
Rainbow Dust makes another appearance in the short story The Wonderful Adventures of Geoffrey Scrutinous.
- Skulduggery Pleasant was the only one to use Rainbow Dust in the series.