Candlesticks in basic charting tools traditionally use either white or green to show an up day and black or red to show a down day. The color of the candlestick is irrelevant to the analysis, but the color makes it easier to detect where opening and closing prices are relative to each other for that day.
The black filled candlesticks indicated that the closing price is lower than the open price. This makes it easier to see that there may have been a down day even though the trend is still buy. If the closing price is higher than the open price, then the candle will be filled with the signal color of BUY (green), HOLD (yellow) or SELL (red) as opposed to referencing a stock’s performance for the trading day. Remember that we are concerned only about the “formation” of the candlestick pattern, not whether the stock has an up or down day.
For the reversal app, the blue bars mean that it is a sell/trailing stop. The green bars mean that it is a buy signal. If a trader has entered the trade on a green buy signal, using the reversal strategy they would exit or set a trailing stop when the signal turns blue.