Actually a couple of things come to mind.
1) spray the inside of the stocker w/ black paint. It should appear glossy due to the reflective-ness of the Plexiglas on the exterior
2) They make a tint spray paint. This stuff can be found in hobby shops and is used in modelling. I'd still spray the inside of the stock screen. I have used this in the past to tint (smoke) clear turn signals. That looked exceptional in quality.
Note: I haven't done either to my windscreen. Yet... But it's in the plan. I'll prob go w/ option 2.
KTM 400 EXC