Hi Rob,
The mono-filament I use for primary rigging (flying wires, landing wires, undercarriage) is 'Steelon' Fluorocarbon coated 0.12 mm diameter.
For cross bracing, control lines and cockpit control lines, I'm using 'Stroft' GTM Silicon-PTFE tempered monofil of 0.08 mm diameter.
Both are installed as they comes, which has a steel like finish, the sheen of which is 'knocked back' by airbrushing a clear semi-matte or light sheen sealing coat.
The photos posted show reflected light, which gives the impression of a metal coating.

The twin rudder control lines with turnbuckles and the aileron control wire horns have been pre-rigged.
The last bit of pre-rigging will be the elevator control wire horns.

Mike