Every country on Earth, for the most part, has evolved a national flag. "It's kind of their one chance to send a nonverbal message to the world, like, 'Hey, we're over here! This is us!'" says James Ferrigan, a vexillologist, which is to say a flag expert and historian.
That desire to be seen, across the land or ocean as well as more philosophically, helps explain why, even though there's no rule requiring countries to develop a flag, they all do it. "No one wants to be left out," he says. "It's almost like we're hardwired for it, you know?"
But choosing a color? That posed a problem, for a while at least.
"Let's say I want to turn this fabric into a new color," Ferrigan says. "How do I do it?" Paint and natural pigments were early options, but these coatings didn't last long. Dyes changed the flag game considerably, but it turns out not all dyes were created equal, which is why we hardly ever see one particular color on flags.
So what is the rarest flag color?
Believe it or not, it's purple. Currently, only five countries out of nearly 200 have purple in their official or co-official flags. "It's exceedingly rare," Ferrigan says.
"Until the 1850s, purple was the hardest dye to produce," says Michael Green, another flag specialist. "It was mainly made by using a sea snail, and it took a ton of them to make even a small amount of dye." Ferrigan says you'd need something like 10,000 of these little mollusks to dye a single garment.
In 1856, an 18-year-old British chemist accidentally synthesized the first purple synthetic dye, but by then the die was cast, so to speak. "Since most national flags were designed before the 1850s, purple was just not a practical color," Green says.
Because of the rarity of the sea-snail dye in ancient times, only the very wealthy had access to it. "So purple was reserved for those who could afford it," Green says.
And the most common?
"Far and away, red," says Green. Red not only represents sacrifice for a country or a cause, he notes, it's also an easy color to produce. "In fact, it appears on over 70% of national flags," he says. Blue comes in second, and white, which is arguably the easiest color to use for a flag, is third.
Primary colors came to dominate because they were readily available and could be acquired locally, Ferrigan says. He gives the example of Denmark's 800-year-old national flag, the oldest in the world, which has a white cross on a red background. The red was probably a vegetable dye called madder, until cochineal, an insect-based dye, was introduced to Europe. Wood pulp, bark and flowers were used for other colors, and indigo, a deep blue dye, spread in the 16th century.
After that, it was off to the races for red, white and blue, in all kinds of combinations. Ferrigan says Dutch ships carried these colors after trying orange and finding it didn't last, and the combination spread from there.
Why not orange?
"Orange is another great example of a color that rarely appears on flags, and for good historical reason," Green says. "It was used, but when exposed to ultraviolet light, the orange colors would fade quickly and turn into undesirable shades." That's one reason orange was swapped out for red back in the early 17th century, though it remains a national color.
Gray, brown and pink are also unpopular national flag colors.