Ehmmm... The truth is that walking today I was thinking about this FX. I had never been able to do it, in fact I thought I should do it by animating it frame by frame, but then I thought about Blender, its UV, a scrolling for its texture in ShaderGraph and a color gradient.
All this was born because only yesterday I learned how to use the 'Custom Data' of the Particle System Inspector, enabling it in the 'Custom Vertex' of the Rendering section.
Happy day :)