I think this tool uses the “reference layer” feature in Clip studio.
https://twitter.com/_oceaninspace/status/1306700485148241921
The equivalent feature in Krita is the ability to filter by “color labled” layers.
Perhaps that could be a feature to add to the colorize mask too someday?
I still think it would be cool to have a “closed gap” detection function added to the bucket tool and even the selection wand and similar color selection tool someday.
If it ever has a real time preview/colorization like this I would use the colorize mask more