First picture is the material function with a working default paint color.
For whatever reason, the material I’m using the function within isn’t taking the vector parameter well. I’m seeing white instead of any color (red pictured), and I’m wondering what the problem might be.
I can’t tell you what is wrong there, but I recreated that Material Function and with Vector3 it works perfectly fine. After switching to Vector4 Parameter, the Color Input doesn’t work, … like in your material.
Edit: Looks like the Parameter breaks something there. A simple Vector4 color does indeed work.