That's a great question with a surprisingly consistent answer across much of the world. If you take a global perspective, the most popular color for public space urban trash cans is overwhelmingly green.
You'll see this from parks in Paris to sidewalks in Singapore. While local variations exist—like New York City's iconic silver "litter baskets" or specific colors for recycling streams—the classic dark green, often in a muted olive or forest shade, is the international frontrunner.
The reasons for this are practical and psychological. Green is strongly associated with nature, cleanliness, and environmental responsibility, which municipalities want to convey. From a practical standpoint, green is a neutral color that blends reasonably well with both urban concrete and natural park settings without showing dirt and grime as readily as lighter colors. It also has high visibility against common urban backdrops without being as visually jarring as, say, bright red or yellow.
Furthermore, this choice is often tied to standardization. Many cities source bins from large manufacturers who offer green as a default, creating a de facto standard. So, while you might find blue bins for paper or yellow for plastic in recycling systems, the general-purpose, catch-all public litter bin is most likely to be a familiar shade of green.