Paint for canopy

That may work well.  What you want is a really deep glossy outer layer.  The black or dark gray represents cockpit surface in shadow, the reflection of the gloss clearcoat simulates the reflection of the canopy surface.  So a really "wet look" clear coat is great.

Thanks for the ideas. Vallejo makes a transparent blue (looks gray) and a transparent smoke that I'm going to experiment with. They might give some depth over something like gunmetal. We'll see.

Google "painted aircraft canopy".  There are some really cool options.  Like Don, I always just painted mine gloss black but some of the newer R/C stuff looks quite convincing.   This one for example uses both black and blue in gloss...

This was a big issue in the days of solid wood models back in days before plastic.  Almost none of the models had cockpits, just a carved bump.  To me gloss black was the most effective color.  Some folks used gloss white, but it was never very convincing.  Many used blue, and it was okay (supposedly reflecting the sky, but plexiglas isn't that reflecting, really).  To me, when you look into a real aircraft cockpit area from above it looks pretty dark.

Keep in mind many AFs started painting black teardrops on bottoms of fighter aircraft in 80s.  It confused opponents in dogfights about which way plane was turning, since the black teardrop looked like a cockpit too.