as shown in the title.
i want to the color of particles change against the density.
the attachment file is my work.but the effect is not good.

Hey I like that!

How about changing the effect by running the attribute through an appropriately shaped function, or a ramp?

very convenient that “add number in proximity”, I had not seen it before.

You can also do that with pointclouds in a vopsop if you wanted to have that kind of functionality in sops. If you combine that with a sopsolver you basically have the equivalent of your particle system, only now it is multithreaded and will run a lot faster.