From Peter Yen of Santa Ana Packaging, a manufacturer of donut boxes:
Anytime you see a movie or sitcom set in New York and a pink doughnut box appears, you know it obviously took place in L.A.
I did not know that! But it turns out that pink donut and pastry boxes are unique to Southern California.1 Why? Long story short, a Cambodian refugee from the Khmer Rouge became the donut king of Orange County during the 80s before he gambled away his fortune in the 90s. When he was starting out he asked his supplier for a cheaper donut box, and the pink box was born. Click the link for the longer story.
1Are they really? Or have they since spread to the rest of the country? Let us know in comments.