If the price is below the oversold level, the candle is colored in yellow.
If the price is above the overbought level, the candle is colored in aqua.
If the price moves back between both levels, no color will be applied.
Might be useful for some of you ;)
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.