In general, passports are only red, green, blue, or black, according to Hrant Boghossian, the vice president of marketing at the interactive passport database Passport Index.
Passports do, however, come in different shades of each of the four main colour groups. "
Within each colour hue, we see vast variations," Boghossian told Business Insider via email. "There are in fact many passport colours."On choice of colours ,he said
For some countries, it's about faith. "Most Islamic states use green passports because of the importance of the colour in their religion," Boghossian said. Green is thought to have been the Prophet Muhammad's favourite colour and U.S. also "a symbol of nature and life," according to Slate's Christopher Beam, which makes the colour "a natural fit for Islam and the Middle East."Other nations opt for styles that reflect their individual character and identity.
He noted that the US had tried numerous colours - red, green, and now blue.
"Passport production is a highly controlled process, and only few companies around the world are doing it," Boghossian said. The cardstock used for passport covers is "usually supplied by a third party" and therefore "only comes in certain colour variations to meet the required standards," he said.