That's a great question that touches on the often-overlooked details of urban design. While you might see a variety of colors, from basic black to safety orange, the most consistently popular and enduring color for public urban trash cans is a dark, muted green, often referred to as "forest green" or "hunter green.
There are several practical reasons for this. First and foremost is discretion. A dark green bin is excellent at camouflaging the inevitable minor scuffs, scratches, and general wear-and-tear of city life. It also does a decent job of hiding dirt and faded spots, meaning maintenance crews don't need to clean them as frequently as they would a bright white or light grey bin. Furthermore, this particular green is chosen for its aesthetic versatility. It tends to blend naturally into park settings with grass and trees and doesn't clash too aggressively with the concrete, stone, and brick common in urban landscapes. It projects a sense of civic duty and environmental consciousness without being loud.
Of course, you will see other colors serving specific purposes. Bright, high-visibility colors like orange or yellow are sometimes used in high-traffic pedestrian areas or near roads to ensure they are seen, thereby reducing litter. Some modern "smart" solar-powered compacting bins are a sleek silver or black to project a more technological, clean image. However, for the standard, workhorse bin found on countless city sidewalks and public parks, the champion remains a humble and practical dark green.