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Strange request, but it would enable fading between two colors using the intuos airbrush wheel -- if the animbrush were, say, a 30 frame transition from a white to a black circle, the brush in Luma Stamp would transition between A/B colors. Nice quick way to do two-tone painting, I think.
I know the math wouldn't always line up, but even an imprecise control here would be useful.

You can assign a hotkey to go to next / previous image in the AnimBrush (Brush : Next/Previous Animbrush).

So, maybe you can assign a hotkey to (imagine) A / B, then, in the Wacom preferences, assign the hotkey A / B to the finger wheel ?

Interestingly, the finger wheel is not customizable through the Wacom control panel settings...
Thanks for the thought, though.
David