These two lines on the graphs are visible when you click the “Show Trends” button on the right hand side of the screen.
The main purpose for this is to show the trends of traffic on the graph. one thing that would need to remember when look at this,it only looks at the traffic that is indicated in the time frame, whether its hourly/daily/weekly.
Orange [bps in trend] represents the trend for the traffic coming in during that period.
Purple [bps out trend] represents the trend for the traffic going out during that period.