This is a very powerful filter, and I use it all the time, especially for adjusting saturation and gamma, but there is one tiny improvement to the interface which I would welcome. This comment applies to the Windows version. I don't know if it is also true of the Linux version. There are no scale marks on the sliders. Even if it was just a vertical line on the slider bars to show where the initial (zero/default) position was of each slider, it would make it easier to judge the amount of effect applied. I know you get all the settings shown as numbers in the active filters list, but scale marks would be a small cosmetic enhancement which I think would be a big usability aid.
Already implemented as a floating label showing the exact slider value, please see https://avidemux.org/smif/index.php/topic,18990.0.html (https://avidemux.org/smif/index.php/topic,18990.0.html).