Marvel of modern engineering and cultural talisman: https://en.wikipedia.org/wiki/Red_Solo_Cup
The colour of these cups is a cultural import from the US; if your frame of reference is the cup's portrayal in media, then the red Solo cup appears to be exclusively used for partying and drinking with abandon (e.g., consider the image of college students playing beer pong), so you get red cups if you're a teenager organizing a party.
Funny enough, the Dutch ones are completely inferior, and way more expensive. They crush easily, don't separate well, and are weirdly small, not to mention several euros for a tiny package. This has annoyed me to the point where I now bring a little stack of Solo cups each time I fly to the Netherlands.
At normal parties in the Netherlands we just drink beer from bottles because we have an entirely different beer and alcohol culture, without the whole age limit BS (despite recent legal changes raising the purchase age to 18).
With the exception of the transparant hard plastic cups used is stadiums and at festivals, we tend to not drink our alcohol from plastic cups.
Now I know. Thanks, internet.