In fact, there is nothing wrong with purple itself. There are several reasons why all countries don't use purple as the flag color. First, purple appears too late. The country with the earliest appearance of purple in the world is China. The purple maid found in Qin Shihuang's mausoleum is the earliest purple in the world, but the production technology of purple has not been handed down, so China has no traditional knowledge about purple. In the west, purple appears very late, so many cultural symbols are not worthy of purple.
When many countries draw national flags, some representative colors will be used on the national flags. For example, red, white and blue are symbols of freedom, equality and fraternity, which have been adopted by many European countries and colonized in America and Africa. Green represents Islam and is used on national flags by a large number of Islamic countries. On the other hand, red represents revolution and is a symbol of many anti-colonial and anti-feudal countries. It can be said that the national flags formulated by many countries in modern times are mostly the product of political thoughts and are represented by several colors. But purple appeared too late to keep up with the pace of various thoughts, so it was not applied to the national flag on a large scale.
Second, purple is too expensive. In the East, if you want to extract purple or color from cinnabar, orpiment and malachite, the process of extracting color is very complicated. In addition, it is a purple pigment extracted from Arnebia euchroma. Craftsmen crush the roots of Arnebia euchroma, add alcohol, cook at 69 degrees, dissolve the purple pigment in the liquid, and filter out the residue to get the purple dye. However, the purple extracted by this method is too easy to fade, and it takes many times to repeat the process before dyeing, which is a lot of work.
The way to extract purple in Europe is mainly from animals. First of all, conch, a conch needs to soak for ten days to extract purple pigment, and the amount of pigment is very small. Even if 2000 conchs were soaked for ten days, only 28.3 grams of purple dye could be extracted. I don't know how many conchs it takes to dye a dress. Another animal is the bone snail. The method of extracting purple from bone snails is more cruel and needs repeated stimulation, but even 250 thousand bone snails can only extract 25 grams of pigment.
It can be said that in ancient times, the price of purple pigment was higher than that of gold, and sometimes even if you had money, you might not get purple dye. Purple also has a high status. During the reign of Elizabeth I, the Queen also ordered that no one should wear purple except members of the royal family. Think about it, the national flag is very big. If it is dyed purple, the cost is unknown. In order to reduce costs, many countries give up purple. Until 1856, British chemist William accidentally produced a purple compound while doing experiments, so he applied for a patent. As a result, purple dyes were produced in large quantities, and the status price also dropped.
To sum up, the reason why purple is not widely used in the national flag is that it appears too late and the cost is too expensive.