Reverse/Inverted Color Key or Reverse Alpha Channel in OBS?

[corbu]

Hi,

I'm trying to achieve some kind of reverse color key effect in OBS.
I'm creating a sort of music education show were I play the piano, and I want to overlay certain colors over certain notes on the camera feed.
That part is easy:

However, when I play those keys on the piano, my hands go underneath the overlay, so you can't see what i'm playing.
I've tried making the overlay more transparent, but that just dulls the colors and still makes it hard to see what I'm doing.

I had the idea to duplicate the camera layer, wear blue rubber gloves, and do a reverse color key on the blue gloves.
This way, the top layer would only show my hands, the middle layer is the color overlay, and the bottom layer is the normal camera view of the piano.

This all works great (the blue gloves are easily picked up by the color key effect), but I can't figure out how to invert the alpha channel on that layer.
Is this possible? Does anyone have any workaround ideas?

 

[Devini15]

Coming back at you from 5 years later because I have the same issue.
I don't have a good way to invert the alpha of a source, but I do have a workaround:
1. Make a chroma key that's as close to the color you're trying to isolate as possible.
2. Copy the hex code of that key
3. Invert that color (subtract from #FFFFFF)
4. Make a new key with the inverted color, turn up the similarity such that all colors except the one you're trying to isolate are gone.

I use this for a channel point reward to invert the key on my green screen.
It's janky and imperfect, but it gets the job done.