Rising is depicted with the color green while falling is depicted with purple.
Lightness of the color is used to depict the length of the window used, darker == shorter in the 2 -> 512 window range.
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.