Before Canberra's lock-down I noticed a well known hardware store had acoustic pin-boards in lime green. I purchased one 1200 x 800 mm ($30) in lime green and found it worked very well as a green screen for video. The board is 9mm thick polyester, and is strong enough to be propped up without needing any framework. But it is a bit small so I have it propped up behind my monitor in my home webinar studio, to provide some sound absorption.
The boards are also available 2420 x 1220 mm ($84.50) which would be better for a screen, but unfortunately they are not colored. I have contacted the supplier to suggest they make bigger panels in green.