Foliage or vegetation variant color technique

Hello, does anyone know about this technique? I’d like to implement it to create variations of my foliage. I found this presentation from UE Japan, and the technique they used is very interesting, but I don’t know what they were saying. I’m trying to find relevant topics to study. Does anyone know the name of this technique or any relevant sources about it?

https://www.youtube.com/watch?v=JBcwRoIwmWo&t=343s