Use Set FillColor and Opacity.
However I would instead make a binding
Then use that to set your color
Im trying to change a health bar from green, to yellow, to red. Ive done this before but cant for the life of me remember how i did it. The parameter name is correct, so is the logic attached to the white pins, i think using get dynamic material from the fill image is the incorrect part. How do i change the color on a material in a progress bar?