Blue Candle represents the Boring Candles ==> Demand and Supply is in balance
Black Candle represents the Exciting Candles ==> imbalance between Demand and Supply
If you are looking for automatic indicator for demand and supply zones, you will have to tradingview home page and in search bar drop down select people and in searchbox "ConfidentSelfTrader", then select SCRIPTS, then click on "Demand and Supply Zones indicator", scroll down and add it as your Favorite Scripts, then you can use "Demand and Supply Zones indicator" for free....
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.
as per version 4 you can replace it with "barcolor( (Body_Range <= Candle_Range * 0.5) ? color.blue : na)"...
All the best.
By the ways, I PM'ed you regarding the demand/supply indicator. Hope you can get back to me, when you get the chance.