McDonald's, Burger King, Jack in the Box... These fast food companies have something in common. Can you spot it?

麦当劳、汉堡王、玩偶匣汉堡店……这些快餐公司有一个共同点，你注意到了吗？

Well, besides all being fast food chains... They're all red. And it's not a coincidence. Color is one of the many tactics companies use to connect with customers. And if swearing off fast food wasn't hard enough, those colorful red logos might make it even harder to ignore.

Fast food companies all use the color red heavily in their logos, why? The answer goes back thousands of years.

The average human can see ten million colors, but red is special. Turns out, it's one of the first colors our ancient ancestors thought important enough to name. Back before alphabets and writing, early human languages were surprisingly... uncolorful. There were words for "black" and "white' and "red" but not much else. In fact, blue didn't show up until thousands of years later in 200 A.D.

As a result, we have a deeper connection to red than any other color on the spectrum and we react to it in certain ways that actually play to fast food companies' advantage. For starters, researchers have found that red can evoke a sense of urgency. On top of that, it also has an innate ability to whet our appetites. And when you pair those two together you've got the perfect recipe to attract hungry customers who want food, fast.

So that red logo isn't just a welcoming sign it's a sly seduction for your brain. Now, it's unclear why red makes us feel this way. But perhaps it has something to do with where the word comes from. Many ancient languages, including Hebrew and from tribes of New Guinea, first named red from their word for "blood."

But red's bloody beginning has transformed over millennia. During medieval times, for example, red was worn by royals as a status symbol. And today, brides in many parts of India are married in red dress.

In fact, red is one of the few colors today that cultures all over the world view positively. And it's no wonder companies dedicate so much thought to their logos. After all, we're a visual species. Despite having five senses, 80% of the information our brains process on a daily basis comes from our eyes.