Black background indicates the sideways movement, you will not find any profitable trades while it is moving sideways. Many investors avoid having long or short positions on sideways movement, as it is not worth to get in. On the bottom of the screen, you will see the long or short indicators as well.
The red line is for bearish and green is for bullish. If the color line is leading up with the trend without touching down on the strength, the demand is a solid trend for the leading color line. Before opening the position, check the leading line above, and last color at the bottom of the screen.
Best way to swing or intraday trade is to open a position when the strength is starting to grow. When it declines, the market tends to go slow, that is where you can take profits when the strength level is below 25. This strength indicator is good for swing/intraday traders within the short time frame. Recommend using it for opening entry for the position on the short time frame and avoid when the market goes sideways.