People feel a lot of feelings about airlines. Usually, they're negative ones -- especially when it comes to the airplane seats themselves. Economy class is cramped, leg room is tight, and the seats typically recline just five degrees.

Airlines are well aware of this. Since  air travel can be anxiety-inducing, airlines spend big bucks on the interior design of their cabins. There's a whole psychology behind how airplanes are designed, right down to the color of the seats.

Ever notice that airplane seats are usually blue? Southwest, American Airlines, and United Airlines all have seats in a shade of blue. From budget airlines like Ryanair and Spirit Airlines to international carriers like British Airways, blue seats are commonplace.

Next time you board an airplane, observe the color of the seats. Here's why they're often a soothing, dark shade of blue.

Blue is calming

Color psychology plays an important role in selecting the fabric for airplane seats. "The idea is to give airplanes a more residential feeling, with relaxing colors and restful designs," explained Shelly Zundell in a Boeing press release. Zundell previously worked for Teague, an industrial design firm whose clients include Boeing. People associate certain colors with certain feelings. Blue is a calming color that suggests peace, serenity, and relaxation.

It physically feels cooler

It's also on the cool end of the color wheel, and can physically make you feel cooler. In a study reported by Popular Science, 48 percent of participants thought soda in a blue glass was more thirst-quenching than one served in glasses of other colors, probably because they associated blue with cold. Likewise, warm colors such as red and orange can make people feel warmer. Although it's not unheard of, red is a less common color for airplane seats. Feeling hot and stuffy when you board an airplane is good for no one.

Blue feels professional

Blue can lower your heart rate, improve mental clarity, and inspire creativity, according to Color Psychology, a website that explores the meanings of various colors. It also says it instills confidence and trust -- something that most airlines could use more of.

Airlines tend to veer toward blue in their branding and seat design because it reflects a cool professionalism. Blue's not too wacky and is one of the more conservative colors, projecting a sense of stability. Another study, published in the Journal of the Academy of Marketing Science, found that people associated blue with competence. You're putting your life and safety in the hands of the crew and the airplane itself. So competence is certainly a priority.

It's a universally well-liked color

You'll be hard pressed to find someone who has strong feelings against the color blue. It's a universal color that's widely appealing to the masses.

This is also the same reason that many brands opt for blue logos. People universally associate the color with positive things -- such as clean water and blue skies -- so they tend to like it. Across ages and across cultures, it's the world's favorite color.

The right shade hides stains well

Dark blue seats are also just plain practical. Imagine how many people sit in them per day. And how many crumbs, beverages, and who-know-what-else gets spilled on them? Darker shades are better at masking stains and don't show their wear as easily. Those dark blue seats will look fresher and newer for longer.

So when you squeeze into your restricted legroom seat, kick back, and recline those measly five degrees on your next flight, know the airline tried to make your flight a comfortable and oh-so-calming experience with color psychology. If the color of the seats isn't doing it to curb your stress, hopefully you're flying on one of the airlines that offer a meditation app.