This is as close as I can get, along the lines suggested.

I can't get any results from the Color Gradient. It only seems to make use of the color at one end of the gradient.

I have created a Mixer with the Colour Channel shader as Source 1, and a color gradient as Source 2, but cannot get any graduation at all. I can get an effect if I use "Brick" or something obvious like that.

Also I'm not sure why the "Color Gradient" requires a Color subshader.

Shader settings:

Still learning this package!

Thanks

R