I've seen AZ DOT running split rotators, amber to the front, red to the rear. It has been almost 20 years since I've seem that though. Red front, amber rear also makes sense for the back of a fire engine. Then there are states like mine, New Mexico. They really don't care what's facing back, just forward (just no white to the rear except work lights). I'm guessing more than half of highway service vehicles here (private and state ran) runs red or red/blue to the rear and amber/blue to the front. That red scares bad drivers over more than anything.
Here in Texas, red is the prescribed color for emergency vehicles, but blue is allowed as an auxillary color only. Blue standing alone is not legal for emergency responses, although I've seen it done more than once. And I've never seen any effort in enforcing it. Clear to the rear is forbidden, but has always been allowed w/o question in the Federal and Dietz "hill lights". The one run-in I had with
law enforcement over clear-to-the rear was absolutely silly. In 1971 we got a 1963 Pontiac Consort ambulance for our standby ambulance service, with which we worked the local car races and other sporting events for many years. Superior Coach provided a manual backup light switch just inside the rear door of its coaches to serve as a loading light. Our '63 Pontiac was so-equipped. One Fri. evening we had transported from the car races to Lubbock's then-Methodist Hospital (now Covenant Med. Ctr.). After the races we were just pulling out of the racetrack property onto the northbound service road when we were suddenly, totally unexpectedly, stopped by a DPS trooper. My partner that night, Henry, was also a police officer at Texas Tech. So when I get out and hand the young trooper my driver' license, he asks if I knew what the speed limit was on the service road. I replied that it was 45 but I had just entered the service road and was barely doing 35 when he stopped us. He went ballistic, hollering at me that I was not to argue with what he was saying I was doing...even though he never said what he had "clocked" us at. So then he says that the reason he stopped us was because Texas didn't allow white lights to the rear. So we walked to the back of the car and the backup lights were on. I knew what it was: that one of us had bumped that inside switch when we had a patient earlier. So I reach inside and flip the switch and the backup lights go off. But the young rookie (as we would find out) just kept on and on and on about the clear to the rear, when finally his sergeant who had been riding "shotgun" steps out and tells the young guy to let it go as we knew the problem and immediately corrected it. And he tells us that we're free to go. All this time neither the rookie or the sergeant knew that my partner was actually a state police officer himself (Texas Tech police had statewide jurisdiction, as did
law enforcement officers from other state colleges or universities). It was all Henry could do to keep quiet. So when I sit back in the driver's seat, Henry tells me to crack my window open and listen. The sergeant had begun chewing on the young rookie trooper for his improper behavior towards me, and went on and on. You could still hear him hollering when we drove off. All of that over a couple of backup lights! Something else here in Texas that's rarely heard about, and that's the current
law that no longer allows "lights only" on emergency runs: either on emergency vehicles or volunteer POVs. Emergency runs have got to be with both lights and siren. I've only seen that new rule enforced once. A then-young guy who was on a neighboring VFD ran only a teardrop light on his
POV and was downright obstinate about not wanting a siren. From where he lived, he had to cross a busy highway on any response he made; and he did so with just the teardrop light on top and honking his horn. He was repeatedly warned by local
law enforcent about what he was doing and he would just laugh at them. That was until he piled us his car crossing that busy highway when someone just didn't his light: and of course, there was no siren. And he was subsequently taken to the proverbial "cleaners" over that one.