In the US for light weight (or simple trailers), federal law
requires trailers to have taillights, brake lights, side marker lights
(or side reflectors) and turn signals (unless the turn signals are
clearly visible from the tow vehicle). This can vary by weight and
possibly by state.
Generally brake lights and running lights to the rear are red.
Clearance/marker lights are yellow and turn signals can be yellow
or red.
