I'm going to admit a partial overstatement on my part. I contacted the motor carrier safety unit in Oklahoma. They stated there is no specific law prohibiting tinted lenses. However it is accepted by courts that tinted lighting devices disrupt minimum photo metric requirements of the lights. You would be hard pressed to find a tint that doesn't, because most stock lights meet minimum standards already. Most officers who are well versed in mechanical violations and FMVSS nomenclature and case law can make a case for a violation of an adopted standard.
The actual wording states (FMVSS 108 S5.1.3) No additional lamp, reflective device or other equipment shall be installed that impairs the effectiveness of lighting equipment required by this chapter.
Understand that this stuff is so far beyond the knowledge of 99% of officers out there...you stand a great chance of never being bothered. Regardless you are cutting into the effectiveness of your lights and real dark tinting is obvious to an officer (well versed in FMVSS requirements or not) making the perception cause for a stop.
I've made a career helping officers make cases and research laws to support their case. Most states specify "no tint" for lenses. At least 27 that I could easily find. However all states adopt Fed regs and the ultimate fall back is the code I mentioned above.
Anyone can read and interpret words to fit their own needs. There are numerous layers to accurate legal research. You start with Federal, State, County Court Decisions and then through various levels of case law as interpreted by municipal, supreme and superior courts. As states face legal challenges and appeals do you find them adopting specific wording to incorporate the law. In my state, tinting lights is specifically prohibited. As well as most of the bordering states. Tinted windows are another issue.
Sorry this is long, but it is a very challenging legal interpretation. Yes...ultimately it seems chicken sh** to get pulled over for it, just don't get pissy. You can probably escape with a good attitude and ignorance. But you can say that it meets the photo metric requirements of FMVSS108 and confuse the heck out of the officer. Though it probably doesn't.