Just a dash of ammonium iron sulfate sprinkles and cosmetic glitter in a test tube of water and potassium hexacyanoferrate. These clear substances combine to form a brilliant Prussian Blue (ferric hexacyanoferrate), the first of the modern artificial pigments, accidentally discovered in 1704, and used as a dye in Prussian Army uniforms.
Oddly enough, this potion recently received FDA approval to treat people exposed to contamination from radioactive cesium-137 or the thallium once used in rat poisons. The Prussian Blue adsorbes the contaminants before they get absorbed into the GI tract, lowering their biological half life. The CDC includes Prussian Blue in the Strategic National Stockpile.
The intense color comes from the absorption of 680nm light in the intervalence transfer band (an electronic transition from a low-spin Fe2+ ion in a carbon-coordination center to a high spin Fe 3+ ion in a nitrogen-coordination center).