These are levels based on volume. The idea is that candles of high volume a higher amount of traders with active long/short positions to either close out, protect, or add to.
A stack of red candles means that area is a point of interest, similar to a VPVR POC.
4pm EST is the end of liquidity for the whole trading day. Study how price oscillates around that price level. Its a magnet prior to US open and after US close. I would suggest adding a few Volume Weighted Moving Averages whose periods are time based. Example: 15minute chart set the VWMA to 96 for one full day. Then a few more, like 192 for two days, 288 for three days and 480 for one full week. This will help see the correlation of Price and Volume trends to and from those 4pm liquidity levels. :)