Those lenses are equipped with a reflective coating on the outside that makes them appear like little one-way mirrors.

Mirrored Lenses

They typically decrease the amount of light by up to 60%.

This option is available in Gold, Silver, Pilot Green (Aviator), Blue and Red.

Mirror lenses have highly reflective coatings applied to the lens, reducing the amount of light going into the eye. They are particularly useful in very bright conditions, like skiing under the sun.

Their popularity with police officers in the United States has earned them the nickname "cop shades"

The color you choose is a purely cosmetic: it will not affect your color perception.