Finally got around to modify the lense on my mask too. I ordered a sheet of self-adhesive film from eBay, normally used for tinting car headlights. It's tinted in dark gray, so no need to paint it. It's a bit thin if you pull off the protection film, so my advise would be to find a clear sheet of plastic (seems easier than finding gray ones) and stick it on there. While I was waiting for the headlight film to arrive (took one month from Hong Kong) I looked for other solutions - the things that came closest to the color was some flexible vinyl ring binders in semi dark gray, but the surface was matte and not nice and shiny as I wanted. So I was glad when the film finally showed up today. Had to make a couple of test fittings before getting the right size for the lense. But here's how it looks now: