Check out Theo's Fusion matte-to-Resolve color page tutorial at MeisnerMedia, along with the comments and suggestions from others on his channel:
Of course, his solution, like all real solutions, seems simple after it is explained. But many hours have been spent trying to get a Fusion matte into the color page and have it actually work.
This is such a welcome solution because it seems that Fusion mattes, such as using the Fusion ChromaKey tool like the qualifier tool in the color page, just sometimes seem to work better. And we can all reasonably suspect that their different algorithms account for this.
The comments by others for this tutorial point out that there is sometimes an alpha premultiply issue affecting the way the Fusion matte is accepted in the color page.
Perhaps some knowledgeable person can clarify this issue and the simplest fix: perhaps just a premult/unpremultiply node before the Fusion MediaOut node???
Simon Ubsdell has a wonderful tutorial on this confusing premultiply issue:
Also a fun channel for Fusion is Vito's Con-Fusion with this tutorial on premultiply
These guys have many other very informative videos on alpha used in blend modes and compositing. So much information that I haven't seen anywhere else. I watch them over and over, learning more each time, as they are very thorough.
Thanks again, Theo and Simon and the Vito the Pirate (great fun pirate voice and a master Fusionist!)