In 2019, I wrote a practical but boring blog post about using the Divide layer mode to extract a Multiply shadow color.
It's one of the things I wanted to eventually rewrite or turn into a short video. Likely next year.
For now though, the above image is the gist of it.
If you want to read the whole article, you can find it here: https://pharan.tech.blog/2019/11/13/color-math-and-layer-blend-modes/












