Sorry, I'm not explaining myself very well.
It's for a Twitch overlay.
So in the background layer, Streamlabs displays the game.
On the layer above it is the HTML5 layer I'm working on. The overlay shows animations, text, etc. Objects move across quickly, and change opacity.
I have it working well enough if I set the background to 255 blue, and chroma/colour key that out, but then when things fade away or are partially opaque, I get this odd blue tint to them.
The example you posted suggested using an alpha image to remove things, which unfortunately didn't work with what I was trying to do.
I've seen people in Streamlabs say that they had issues with this before, but I can't tell if the problem is with C2 or Streamlabs, as I have another program that is working perfectly fine with transparency.