Wis. Stat. § 347.17: Color of clearance and marker lamps and reflectors.

Whenever a vehicle is equipped with clearance lamps, sidemarker lamps or reflectors:

(1) Those clearance and marker lamps and reflectors mounted on the front or on the side near the front of the vehicle shall display or reflect an amber color;

(2) Those clearance lamps and marker lamps and reflectors mounted on the rear or on the sides near the rear of the vehicle, or on both, shall display or reflect a red color.