This volume indicator measures the volume for each bar at the time of day and displays the average and +1 standard deviation above that average. The color intensity of the bar is increased when the volume exceeds +1 standard deviation.
See how on the chart that other than the early morning and late day volume, there are clearly key moments in the day at 7am, 10am, 10:30am, and 11am. See how on the second day, there were volume spikes before 10am, 10:30am and then more obviously just before 11am.