I don't know if this is a bug, but the material "Universal Render Pipeline/2D/Spine/Sprite" checking the "Tint" option turns the skeleton into a colourful disco party. I was trying to create a white "Hurt Flash" effect, using Material Blocks etc but noticed that the Tint doesn't colour correctly.
I was expecting a fully black color to not do anything, while a white color makes the character fully white.
Edit: Using latest versions of Unity 2023.1.9f1, and spine-unity-4.1-2023-08-21
Edit 2: Noticed there's "Overlay Color" if I enable "Color Adjustment", will try to use that for hurt flashes instead. Let me know if it's a bad idea...

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    Note that the option is not called "Tint" but "Tint Black" which supports Slot Tint Black functionality (see here). So you need to enable Advanced - Tint Black at the SkeletonAnimation component as well, otherwise the vertex data is missing and random uninitialized colors will arrive in the shader.

    PeterBacall Noticed there's "Overlay Color" if I enable "Color Adjustment", will try to use that for hurt flashes instead. Let me know if it's a bad idea...

    I don't see a reason why that would be a bad idea 🙂.