Vray Sphere Fade Blend Color Removal in Compositing Software (Fusion)

[Robert1977]

Hi,
this might be a ridiculous question so somebody, but I have no clue how to remove the fade color from a vrayspherefade in an accurate way in a compositing program like Blackmagic Fusion.
Is there an acurrate way how to remove the default grey color with the help of the alpha-channel, or should I switch to black background?
I tried a lot of nodes, but no way is working without remaining artefacts or if I adjust the blending or anything else.
I also read about this in the forum, that Photoshop could do the job if the background is black, but it should work with grey also? Do I need a matte-keyer?

Thanks in advance
Robert

Edit: I doubt that this is the accurate way, and there remain some artefacts:

[Robert1977]

I am impressed, just setting the background color to black does the job, no further compositing necessary.