Format line from time series chart

Hello.

I have a time series chart with a 30-day history of a property, and a target value. I want the line to be coloured differently when it is above/below the target. The State Formatting option only colours the marker from the data point, but not the line.

Does anyone know how to colour the line? My purpose is to have it like this:

Red line when below the target

Green line when above the target

Thank you