Have you ever noticed pickup trucks with big yellow, emergency-vehicle-style lights on their roofs? These might be emergency vehicles. But because yellow is the least-regulated color of warning lights, it is more likely you were looking at a tow truck, a plow truck, or just a truck modified by its owner to be more visible.

Are yellow rooftop lights legal?

Most states restrict the use of blue and red lights to emergency vehicles. But most states allow owners to install yellow flashing lights on any vehicles. Some states do not allow drivers to use these lights on public highways and certain states–such as California–prohibit rooftop lights of any kind on private vehicles.

RELATED: Why Do Some Semi Truck Tires Not Touch The Ground?

What is important to know is that there is no nationwide, federal law regulating emergency lighting. This is why some state police use blue lights while their corresponding fire departments use red lights. But in other states the police use red emergency lights while fire trucks use blue–according to DayWireless.com.

What does this mean for yellow lights on the roof of private pickup trucks or cars? The legality of installing and using yellow lights is entirely dependent on state and local law. So if you are considering a flashing yellow light for your vehicle, definitely read up on local laws.

Want to know more? Found out the color of police and fire lights in every state.

What types of flashing yellow lights can truck owners buy?

There is a huge range of flashing yellow lights that people install on their trucks. The simplest solutions include a spinning yellow light you can plug into a 12-volt outlet and magnetically attach to your roof, when needed. More complex systems are LED light bars integrated into an aftermarket truck body.

The flashing yellow warning lights truck owners choose to install depend on their budget and how much visibility they need. For example, a pickup truck owner with a snow-plowing route might invest in a small yellow light they can magnetically stick to their roof while plowing after dark. This could prevent a negligent motorist from hitting them as they back out of a driveway.

On the other end of the spectrum, owners of towing companies may invest in a heavy-duty truck with a custom “rollback” body capable of loading a wrecked car and hauling it down the road. Because these trucks may work accident sites, many of these custom wrecker bodies feature a professional-grade flashing LED light bar integrated into the rollback.

Learn more about when its illegal to install yellow lights.

Are solid yellow rooftop lights legal?

You may have also seen pickup trucks with a row of non-flashing yellow “marker lights” on their roofs. These lights imitate the markers legally required to warn motorists of an oncoming semi truck’s size. They are not necessary on most pickup trucks, but are legal in every state besides California.

Have you ever seen a large pickup truck with a row of solid (non-flashing) yellow lights on its roof? These are marker lights designed to increase the visibility of an especially large vehicle. On semi trucks, they are always used alongside “marker lights” illuminating the outside corners of the big rig. But on pickup trucks, these marker lights are rarely required. In this case, installing them is a stylistic choice made by fans of the “big rig” look.

Next, read why some factory-built pickup trucks have yellow lights set into their grille or watch yellow rooftop pickup truck lights in action in the video below: