From Traderpedia

Dark-cloud cover is a bearish reversal signal. In an uptrend, a long clear (white) candlestick is followed by a long solid (black) candlestick that opens above the prior clear (white) candlestick's high. The second candlestick must close well into the first candlestick’s real body. The large solid (black) candle casts a dark cloud over the preceding bullish trend. To create this pattern, the following candle must open at a new high and must close below the midpoint of the body of the preceding candle.