Well, material has two constructors... Material(Shader shader) and Material(Source source). The first one, creates a new material with a given shader and second one creates a new material with properties of a different passed in material.
I have done a simple action with the first constructor... It's attached to this post, see if it works as it's my first attempt at playmaker actions.
Make sure your shader is in Resources/Shaders
And then put the name of the shader in the "shader"
and in path put Shaders
The reason I've done this because function shader.Find only works in Editor and not in built game.