Something to keep in mind about tinted canopies. A tinted canopy (or sunglasses for that matter) result in less light reaching your eyes. Less light will result in lower visual acuity. I for one, want as sharp as possible vision when I fly.
From Wikipedia:
20/20 is normal (daylight) vision. In low light (i.e., scotopic) vision, spatial resolution is much lower.
From personal experience, I use the least amount of tint on sunglasses to get the job done when I fly or drive. For other applications such as kicking around the beach where I have less need of sharp vision, I go with a much darker tint.
Perhaps someone with the proper background could elaborate.