Why do passports around the world only have 4 colors?

It is a fact that all passports in the world are only specified in 4 main colors, and why is that?

Passport is one of the important identification documents of citizens. When going abroad, no matter where you go, you should bring your passport with you, it is like a standard travel ticket, a protection of rights for each person when setting foot in a strange place. And you know, almost all passports in this world are classified into 4 main colors: black, green, red, dark blue.

In addition to the fact that countries must comply with the passport size, the color is the choice of each country but is within the 4 main colors mentioned above. Some hypotheses about the choice of passport color are explained quite reasonably as follows:

Red:

EU countries often choose burgundy for their passports. It can be seen that this common color represents a collective spirit. Recently, Türkiye also changed the color of its passport to red to express its desire to join the EU.

Another hypothesis is that red was favored by the Nordic countries because it represented the brilliance of the Viking era.

Countries with a tendency like Slovenia, China, Serbia, Latvia, Romania, Poland, Georgia also favor red on their passports.

Green:

Muslim countries such as Morocco, Pakistan or Saudi Arabia are very fond of this color. Maybe because this is the favorite color of the leader Muhammad in the Islamic Bible, the shade has the meaning of spirit and life. That is why we can easily see this green color in most Muslim countries such as Iran, Pakistan...

Dark blue:

Represents the community of New World nations such as North America, South America, Oceania...

This color is also used as a system in the Caribbean Council member countries, to show their geographical location near the sea.

Some countries associated with the Mercosur Customs Union also choose this blue color to express the spirit of connection such as Brazil, Argentina, Uruguay, Venezuela...

Black:

Black passports are the least common of the four colors, and are issued by African countries such as Chad, the Democratic Republic of the Congo, Zambia, Botswana, Burundi, Gabon, Angola, and Malawi; or by countries where black is dominant, such as New Zealand. In the United States, black passport holders are granted diplomatic immunity, and airport officials do not have the right to search, delay, arrest, or detain them.

According to Young Knowledge