Typically in Krakatoa for Maya/3dsmax, you could do this using our Magma operators, but unfortunately, the C4D version of Krakatoa does not provide Magma.
So, there isn’t really a standard way of doing this in Krakatoa C4D. One idea that might work is to create a PRT Volume from the fluid mesh, and set the color of the particles to black. That would essentially provide some attenuation of your non-black particles that are deeper inside the mesh. I actually am not sure if this is a practical approach, since you would have to set the density of the black particles fairly low, and have a really dense set of particles, but it may give a decent look. It would give you a strange alpha channel though.