I've got 3% tint on those windows, so it's hard to notice anything.
But I checked. General rules: http://www.dmv.ca.gov/pubs/vctop/d12/vc26708.htm
This is the exemption:
(b) This section does not apply to any of the following:
(8) The rear window or windows, if the motor vehicle is equipped with outside mirrors on both the left- and righthand sides of the vehicle that are so located as to reflect to the driver a view of the highway through each mirror for a distance of at least 200 feet to the rear of the vehicle.