Ben, I got my info from Websites that purport to give the tiniting laws for various states including CA.  After your post, I looked it up in the Vehicle code to verify the websites information.  Section 26708(d)(1) of the Cal. Veh. Code states that transparent material may be installed on front side windows provided " the material has a minimum visible light transmittance of 88 percent."
Anyway, 88% is basically clear, so I would say johnny law would probably jump on anything that looked tinted.  But then again, you see them everywhere.  Charlie.

<< Not true -- Ca allows tint on front sides at 88% Lt -- which by the way is
 almost clear -- maybe that was what the shop was saying.  Charlie. >>

Both my law enforcement contacts in California advised me that "ad-on" tints
(film or spray) is not permissible on the front side windows. I was also told
that tinting is allowed when incorporated into the glass (ala OEM). Even that
has to be very light. I don't have the exact percentage at this time.

Rear window tinting is permissible as long as the vehicle is equipped with
both side mirrors.

BenT
San Francisco