After some time dithering and a bit more practice on scraps, I decided the only thing was to go for it so I have painted the back of the folded patchwork cushion which I had already free motion quilted. I used a slightly furry roller, not the dense foam as recommended by Linda and Laura Kemshall because that seemed to give a to solid effect. It looks OK and doesn't obscure the nice purple fabric underneath. I don't quite get the point if the carefully chosen fabric gets obscured. Also I chose a fabric paint as that leaves the work softer to handle and washable unlike acrylics. A stiffer effect using acrylics has its place but not here. In my enthusiasm I didn't take a before picture, here is the after. The paint is silver though it looks gold on the photo.
Lastly I have undone the free motion bag with the raggy effect block assembly as I decided that I really didn't like that way round. It will be reassembled rights side out, raw edges on the wrong side and those edges maybe bound or just zig zagged. Back to the machine for the reconstruction