ferric ferrocyanide

What it is
Ferric Ferrocyanide, also known as Iron Blue, is a is a synthetic dark blue pigment.

What it does
Ferric Ferrocyanide is used as a colouring agent in cosmetics, including those for use around the eyes.

Side effects
Ferric Ferrocyanide is generally considered to be safe.

(Source: cosmeticsinfo.org)