Unfortunately, as a sworn official, the cops word will be golden...I don't think he will have to "prove" anything. Just like a speeding ticket, the cop will say "I paced him going XX MPH or the radar said XX" Sure, you could call his credentials into question, but in the end it's just his word saying "I saw this" and that is good enough. He can just show up, say "It was tinted" and the ball is in your court...guilty until proven innocent.
Best case scenario is you probably take a day off work, go to a tinting shop, have them look at it and write a ticket (or better yet a sworn affidavit) saying there is no tint on the front windshield, then take another day off work and go to court, plead not guilty and get a trial date set, then take another day off and go to trial (hope the cop actually shows up, or the judge may decide to continue the case to a later date). Hopefully the judge is sympathetic and rules in your favor.
So, you do all this running around, extra gas, time off work, etc and hopefully you will beat the ticket! It's great in principle, and it would be even better to see the cop on the way out and tell him "Thanks for nuthin' Di@%"
The flip side of the coin is that it is probably a sub $100 ticket? and most likely not a moving violation, so no points on the license, no insurance worries, etc. You'll have to weigh all your running around versus just doing as the man wants..."Pay up sucker!"
Definitely let us know how it goes, though!
PS - for the record, my 99 has a very slight green tint to the windshield and a slightly darker band about 3-4" down from the top. But the dealer said it was replaced when I bought my truck, so it is aftermarket.
Corey