I’m in Unity 2021.2.12f1 and for the past days I have found no fixes for this. I am using the URP>Particles>Unlit shader with Alpha blending mode + Multiply Color Mode, and for some reason when particles are getting more transparent, they also lose more and more of their colors, as if they were also fading towards white. What is the reason behind this? My grayscale sprite is imported correctly with Alpha Source from Gray Scale and Alpha is Transparency checked.
There is an issue currently that HDR on URP is only 32 bit, creating all sorts of issues with color quality and so on. There is a solution already implemented internally at Unity ([URP-220] Add URP backbuffer HDR format options by eh-unity · Pull Request #6728 · Unity-Technologies/Graphics · GitHub) and we are now waiting for that solution to be added to a Unity build.