When a down candle (black or red) opens above the close of the prior up candle (white or green), then closes below the midpoint of the up candle, the dark cloud cover pattern is created.
The Dark Cloud Cover pattern on a Japanese candlestick chart indicates a potential bearish reversal.

Because its formation reflects its name, this candlestick pattern is easily recognizable.

A black candle signals a trend reversal at the end of an uptrend (a "sunny day").

Piercing (which is a bullish reversal candlestick) is the opposite of Dark Cloud Cover.