Why can you only see shades of grey in dim light?

In dim light, the cones in our eyes, which detect color, are less effective, while the rods, which are more sensitive to low light, become more active. Rods do not perceive color but are highly sensitive to light and movement, allowing us to see in shades of grey. This is why our color vision diminishes in low-light conditions, resulting in a grayscale perception of our surroundings.