While looking into sound suppression films for glass, I stumbled onto this valuable little gem - a matrix chart by the International Window Film Association, which lists the various window tint regulations, state by state.
This includes such information as what colors of tint are allowable, if metallic tints are allowed, which windows can be tinted and what percentage transmission per window, and what percentage reflectivity is allowable. And also, whether medical exemptions are allowed. Good stuff to have a clear idea of before becoming potential traffic stop bait!
http://www.glassessential.com/images/stories/Solar%20Control%20Film-Auto/US_Tint_Laws_IWFA.pdfThere's also some info for the Canadian Vanners, though it's not as detailed. Lucky Canadians - not so many micromanaging local governments trying to cash in, eh?
http://www.glassessential.com/Window-Films/window-tinting-laws.htmlThere's some other useful info on the site, like care and installation tips, and also info on automotive UV and IR rejecting window films - good stuff in my book, and well worth investigating further!
Clear skies!