Pongee Lining Fabric in lime color ($8 per m). This was held up with clothes pegs, and worked well.
Also I tried "PPE Moulded Fabric". This is far stiffer, harder to hang, and the color did not work as well. This is a non-woven polyester fabric similar to that used for reusable supermarket bags. I am not sure about the claim it is suitable for Personal Protective Equipment face masks.