The GREEN AREA represents advancing issues. The INTENSE GREEN AREA represents the advancing issues at daily high.
The RED AREA represents declining issues. The INTENSE RED AREA represents the declining issues at daily low.
The part above the BLUE LINE represents issues which are trading above their VWAP (volume-weighted average prices).
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.