How to understand “Cd” and “diff” attribute?
In my view,the “Cd” is hardware color,the “diff” is software(renderable) color,but renderman may render the “Cd” attribute.

The only thing that matters for rendering is what the shader understands. So, if your shader (in PRman, or Mantra) has a parameter named “Cd” then the attribute called Cd will render.

Cd is special in Houdini in that the OpenGL viewport recognizes it (either as a point or primitive attribute) and uses it to render the geometry in the viewport.

You can have any attribute on geometry and as long as the shader has a parameter with the same name and type it will render.

Cheers,

Peter B