What Color does Tiffany and Co. use?

Tiffany blue.

The Tiffany Blue color is protected as a color trademark by Tiffany & Co. in some jurisdictions including the U.S.[1][2]

The color is produced as a private custom color by Pantone, with PMS number 1837, the number deriving from the year of Tiffany's foundation. As a trademarked color, it is not publicly available and is not printed in the Pantone Matching System swatch books.