Cal. Veh. Code § 25282

Any vehicle owned or operated by a contractor or a construction company licensed to operate in this state pursuant to the Business and Professions Code may display flashing amber warning lights to the front, sides, or rear, if the vehicle is engaged in any phase of a construction project performed on a highway, or in the vicinity of a highway, and the vehicle is parked on the highway or moving at a speed lower than the normal flow of traffic. The use of, or absence of, amber warning lights as authorized in this section shall not serve as the basis for any civil action, a defense to civil action, or establish negligence as a matter of law or negligence per se for comparative fault purposes.