From what I can see, all UI Image elements get linked to a Polyspatial object that uses a MaskingShader shader.
This shader uses a color field derived from the color field of UI image.
Is there any support coming for using Vertex colors instead of a field?
Our project creates additional verts for UI images in OnPopulateMesh() to render outlines, storing the color data in the vert color stream. I have tested a local embedded polyspatial package were I’ve modified the MaskingShader as such and it works as I would expect: