There is a special grade of gold called "Blue Gold"!
I received an email from Andersen Genève about Blue Gold.
Below are some extract of the email and there are self explanatory.
"Blue Gold is made of 21ct pure Gold (Au) and 3 parts of iron (Fe). Once chemically combined after a secret process, it has a metallic white gold outlook. A very delicate heating process will turn the precious metal into a beautiful blue colour."
"Aging processes have been conducted to test the stability of the colour. After 300 days under the Morocco Sunshine, the Blue Gold didn’t change its original colour. Therefore the colour of Blue Gold dials won’t vary over time and is guaranteed for centuries"
More details please find the link here
http://www.andersen-geneve.ch/