After years of debating how driverless cars should tell the world no one is at the wheel — flashing text, audio alerts, custom lights — the feds just stepped in with a single answer: cyan.

The National Highway Traffic Safety Administration released proposed changes to Federal Motor Vehicle Safety Standard (FMVSS) No. 108, specifically rewriting the rules to fit autonomous vehicles. It’s a mix of cutting red tape for human-free designs and standardizing how robotaxis communicate with the world around them — starting with a distinctive blue-green light.

NHTSA is proposing cyan-colored marker lamps “to clearly and consistently signal to law enforcement and other road users when an automated driving system is operating the vehicle.” Why cyan? The auto industry already uses red, amber, white, and flashing blue / red lights for such things as brakes, turn signals, headlights, and emergency vehicles. Cyan could theoretically fill the visual gap without confusing road users.

And there’s some precedent, too. Mercedes-Benz got state-level approval for turquoise lights on its Level 3 Drive Pilot cars — even though the automaker has since scrapped the idea in favor of a Level 2++ system. Nevertheless, NHTSA wants to set a national standard that robotaxi operators like Waymo, Nuro, and Zoox, as well as automakers like GM and Mercedes, can adopt uniformly.

Under the proposed rule, cyan marker lights would be optional for manufacturers. However, by creating official federal standards for their color, brightness, and location, NHTSA wants to make sure that any automaker who chooses to add them uses a consistent, legal setup instead of a confusing mix of different colors and signals.

AV operators praised the proposal as an important step towards making the technology more widely available. Waymo spokesperson Dana Gallagher said the company welcomes “NHTSA’s efforts to standardize regulations and remove requirements that don’t apply to vehicles designed without a human driver, while maintaining strong safety oversight.” And Nuro’s chief legal and policy officer James Owens said, “Clear, technology-neutral rules are essential to safely bringing AVs to more communities, and we see this as a positive step towards a federal framework that supports safety, innovation, and responsible deployment.”

NHTSA is also proposing to get rid of some lighting requirements that wouldn’t make sense for a vehicle without a human driver. Current rules demand physical hazard switches, manual beam shifters, and turn levers inside the vehicles. The agency is proposing to remove these requirements, while also updating the 12.8-volt testing standard so automakers can build around modern LED architectures without jumping through administrative hoops. And NHTSA is considering getting rid of requirements dictating whether high-beam lights sit above or below low-beam lights.

This update is part of the broader administrative push by the Department of Transportation to streamline AV deployment. The government wants to make it easier for automakers to build cars without traditional controls, like steering wheel and pedals, that are meant for vehicles that are operated by human drivers.

That said, regulators are also still enforcing the rules as they’re written. Last month, NHTSA opened an audit query into the Tesla Cybercab “to examine the process and technical data on which Tesla relied when certifying the Cybercab and related issues.” At issue is the absence of certain design features such as sideview mirrors, pedals, and steering wheel — all of which are required under FMVSS.

Update October 26th: Updated to include statements from Waymo and Nuro.