The below was copied from the California Highway Patrol's web site
www.chp.ca.gov/html/answers.html
Can I put after-market tinting on the windows of my vehicle?
The main requirements for legal window tinting in California are:
The windshield and front driver's side and passenger's side windows cannot receive any aftermarket tinting.
If the rear window of a vehicle is tinted, the vehicle must have outside rearview mirrors on both sides.
The law prohibits any person from driving any motor vehicle with any object or material placed, displayed, installed, affixed, or applied upon the windshield or side or rear windows, with certain limited exceptions.
However, legislation signed into law effective January 1, 1999, exempts from the above prohibition specified clear, colorless, and transparent material that is installed, affixed, or applied to the front driver and passenger side windows for the specific purpose of reducing ultraviolet rays. If, as, or when this material becomes torn, bubbled or otherwise worn, it must be removed or replaced.
I have received a citation from the CHP in the past for window tinting. Once you receive a citation, you must remove the tinting and have a law enforcement officer from the State of California sign the reverse side of the citation. By the officer signing on the reverse side of the ticket means he has noted the correction made and the driver has complied with the citation. This type of citation is commonly known as a "fix it ticket". The violator then takes the signed off citation to the court where he or she must appear and pay an administrative fee. End of story. If you fail to do the following your registration will be held back by DMV, renewal of your license will be held back by DMV and a bench warrant would be issued for your arrest.