That's a great question! From walking through countless city parks, streets, and public squares, I've noticed a very clear trend. While you might see a variety of colors, two shades overwhelmingly dominate the urban landscape for outdoor trash bins: dark green and various shades of gray (including charcoal and black).
The preference for dark green is deeply rooted in tradition and function. It's a color that blends naturally with park greenery and tree-lined streets, making the bin present but not visually intrusive. Psychologically, it subtly signals "receptacle" without being jarring. The darker hue is also incredibly practical, as it hides scuffs, dirt, and minor stains far better than a light color, requiring less frequent deep cleaning to maintain a decent appearance.
Gray, particularly a matte dark gray or charcoal, has become the modern standard for many municipalities. It projects a sleek, neutral, and professional look that fits contemporary urban design. Like dark green, it's excellent at concealing wear and tear. In more upscale or formal districts, you'll often find bins in brushed stainless steel, which is essentially a metallic gray. These offer a more premium aesthetic while maintaining the same practical advantages of stain hiding and durability.
You might occasionally spot brown bins for a rustic look or specific colors for recycling streams (like blue for paper), but for general-purpose litter, dark green and gray are the undisputed champions. The choice ultimately balances visibility, aesthetics, integration with the environment, and sheer practicality for the hardworking public works crews who maintain them.