Simple.
NYSE only.
0930am-1130am only.
The colors are based on the popular Zanger Ratio.
The code compares the current volume (5m candles) to the average of precisely the same candle on the same day over the past 20 trading days.
Below 60 = drying up / low (grey)
Above 60 = below average (orange)
Above 80 = average (pink)
Above 120 = High (magenta)
Above 200 = Extreme (red)
The example you see is in Central time.
Contact me if you are interested.