That's a fascinating question that touches on urban design, practicality, and even psychology. If you take a walk through major business districts from New York to Shanghai, you'll notice a surprisingly consistent trend. The most popular colors for public trash cans are overwhelmingly dark green, gray (often charcoal or gunmetal), and black.
The reason is a careful balancing act. Business districts prioritize a clean, professional, and uncluttered aesthetic. Brightly colored bins would compete visually with storefronts, signage, and advertisements. Dark, neutral tones like green, gray, and black help the bins blend into the urban landscape, receding visually rather than becoming focal points. They are also chosen for very practical reasons: these colors are excellent at concealing scuffs, dirt, and minor stains, maintaining a "cleaner" look for longer between cleanings. Dark green, in particular, has a traditional association with public service and parks, giving it a subtle, accepted civic presence.
You might occasionally see stainless steel or dark blue bins in more modern, designed-focused districts, but the neutrals reign supreme. It’s a conscious choice by city planners: the trash can’s job is to be functional and hygienic, not to draw attention to itself. So next time you're in a downtown area, look down—the humble trash can is following a strict, if silent, color code.