I love split domes!
At one point ('80s), Mass DPW supervisor trucks had a pair of Whelen "classic" F-heads on a crossbar with a split B/A on the driver's side (blue facing rear) and full amber on passenger. I don't recall ever seeing that on the plow trucks though. @dmathieu - Thanks for sharing!
I'm also from Mass, and never saw the blue used on DPW. I remember Amber both sides of the crossbar. I wonder if it was a one off for some reason. Mass was amber front, red rear in the 50s-60s. In 90s-00s, I remember some clear to the rear.