Unfortunately the UI material is very limited in comparison to the “normal” particle material. The way it works right now is by using the SMeshWidget which only supports FSlateVertex which limits what data can be send to the material. Because of that I can’t pass most of the particle data in (things like ParticleRandom, DynamicMaterialParameters, …). That’s the reason why you can’t even use particle color, but I have to convert it to a vertex color, which limits it to 8 bits per channel.
There’s one thing that could help you with the Dynamic Material Parameter. As a workaround for sprites, I’m sending the first Dynamic Parameter R and G channels to Texture Coordinates with Coordinate Index 1. I know that It’s not ideal, and it’s very limiting, but that’s the best I can do for now.