If you have partaken in an adult beverage at a party within the past 35 years or so, odds are it was in a red cup. Their ubiquity in real life is only surpassed by movies and television, where these cups are guaranteed to make an appearance at any house party scene. So, why exactly did we all agree on red? Or was that decision already made for us?

First, let’s quickly get to know who would have possibly made that decision: The leading producer of party cups is Solo. The Solo Cup Company was created in 1936 by former Dixie Co. employee Leo Hulseman, and got its start marketing the small paper cone cups for water coolers in the 1940s. In the '50s, they brought wax-lined cups designed for fountain sodas into the world. Then, in the '60s, came the funnel-shaped Cozy Cup creation for coffee. And in the 1970s (the exact year is unknown), the red solo cup was first marketed as a recreational drink container.

Sixty percent of Solo party cup sales are for the red variety, and red has been Solo’s best-selling color since the beginning. There are many theories as to why. Kim Healy, the VP of consumer business for Solo, was only able to confirm as fact that they were the first company to introduce a party cup before saying, “I’ve been here 12 years, and I’ve tested this over and over. Consumers prefer red, and it’s not very close. I think for one thing it’s a neutral color that’s appealing to both men and women. It’s also just become a standard.”

Via recent e-mail inquiry, a Solo employee also theorized that red’s gender neutralness was a key factor. Some believe that red’s signification as a color with intensity and energy might play a part, which might explain why Solo turned its original, almost maroon red cups into a brighter red as time went on.

Three different websites that sell “American Red Cups” to American theme party-seeking Europeans all give the same definitive reason: opacity. “The question is why are the cups red?” Americanpartycups.com asks itself in the FAQ section. “Well, if you had a clear cup you’d be able to see what was in your cup, so by making it red you can then easily conceal what you’re drinking. It’s as simple as that!”

If only it were that simple. Plenty of other colors besides red can hide what liquid is in your cup. Modern partiers may simply be copying what they had seen at the movies—the 1999 romp American Pie is credited for being the first movie to portray red cups as a staple of American parties.