- Colorhold makes everything monochrome, even the color I chose to keep.

Finally managed to test Colorhold. The way to get it to work is to use the color picker in the Compositor to get an exact hex value number on a specific spot. Use this for the "color" value. Then you can use "similarity" or "blend" slider to expand that particular color to color values that are numerically close.

- Dedot, no matter how much you change the parameters, shows no difference.

- Maskfun shows no difference.
- tpad do not understand how it works

I did not understand any of these so did not test.