To borrow from another site:
Wearing a solid color at night actually makes you more visible, as it defines your silhouette against a non-solid color background. The average nighttime environment isn't actually solid black, but rather a combination of various dark shades. Another aspect to take into consideration is how solid black shows up in a near infrared camera, which is often used at night in military operations, as well as by hunters and at paintball games. Solid black appears as bright white in a near infrared camera, making the wearer stick out more than if they were wearing duller shades.