Black ice is a transparent coating of ice, found especially on a road or other paved surface.
It typically forms when light rain or drizzle falls on a road surface that is at a temperature below 0 °C. Since it only accumulates in a thin fashion it is highly transparent and difficult to see.
When the temperature is below freezing and the wind is calm, such as under a high atmospheric pressure at night in the fall, a thin layer of ice will form over open water of a lake. If the depth of the body of water is large enough, its color is black and can be seen through the ice, thus the name black ice.