The Treskilling Yellow is a rare 1855 postage stamp from Sweden. Meant to be in a blue-green colour, it was mistakenly printed orangish-yellow. In 1996 the stamp sold for $US 2.3 million at auction; it was sold again, for at least that sum, in 2010. ...
• (n.) An advocate for a metallic currency, or a paper currency always convertible into gold.
Bul'lion·ist noun An advocate for a metallic currency, or a paper currency always convertible into gold. 
a person who advocates a system in which currency is directly convertible to gold or silver.