Why do passports in the world only have 4 colors?

Passport is one of the most important documents for all citizens, especially when you are abroad. Because it is the standard travel ballot, a "card" protects our interests when we arrive in another country. Besides having to comply with passport size, countries can choose their own colors but must be in 4 main colors: black, green, red, dark blue. Why so?

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Some assumptions about the color of passports are reasonably explained as follows:

Red:

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EU countries often choose red wine for their country's passport. Collecting this color clearly shows the collective spirit. Member countries wishing to participate in the block also choose this color.

Another assumption is that red is preferred by the Nordic countries because it manifests the veneration of the Viking era.

A country that tends to like Slovenia, China, Serbia, Latvia, Romania, Poland, Georgia also likes red on their country's passports.

Green:

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Muslim countries like Morocco, Pakistan or Saudi Arabia use green passports because this is a color that is important for their religion. This is the favorite color of Muhammad's leader in the Muslim Bible, the nuance carries the meaning of spirit and life.

Muslim countries like Iran, Pakistan . also choose this color because it is also a color that appears much on their flag.

Blue:

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Expressing the community of New World countries such as North America, South America, Oceania .

This color is also used as a system in the member states of the Caribbean Council, in order to represent its maritime geography.

Some countries such as Brazil, Argentina, Uruguay, Venezuela . are associated with the Mercosur Tariff Union, which also selects this green to show the spirit of connection.

Black:

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It is the least chosen of the four colors, belonging to African countries like Chad, the Democratic Republic of Congo, Zambia, Botswana, Burundi, Gabon, Angola, Malawi and other countries where black is the host religion like New Zealand.

Particularly in the US, black passport holders representing their diplomatic immunity, airport staff have no right to search, delay, arrest or detain them.