Unity Shader Graph, set blackboard properties from code

I have a Shader Graph shader with a blackboard property that I want to change from within my code. The property is called Highlight here are the things I have tried:

Color myColor = new Color(1f,0,0,1f);
material.Color = myColor;                       // throws error (as I expected)
material.SetVector("Highlight", myColor);       // Name in blackboard window

material.SetVector("HighlightColour", myColor); // Name in material property
material.SetVector("Color_8C3A526", myColor);   // Name in the shader inspector

None of these work.

Here's the shader set up: