As for the commissioner's exception, read the law very carefully, it says "the commissioner", which under NYC vehicle and traffic law is defined as the commissioner of motor vehicles, and has nothing to do with any fire commissioners, so technically, the blue light on the squad is illegal.Everything continues to looks amazing as usual.
As for the blue light...Probably a deliberate cosmetic change to distinguish the truck. Just like the FDNY trucks with Qs, and the worst is E-43's black stripe. There is also an exemption in the traffic law where a commissioner can wave the rules for blue lights.
For those that don't know, when used in US fire services the green light is traditionally used to signify a command unit.
In the case of the green command light, that's actually a new nationwide thing. In New Yrok it's a little weird since my local vfd is getting their new cheifs' cars with a green light on them but my ambulance corps also runs green lights as a courtesy light, so now we have multiple agencies running vehicles with green lights for different purposes and it gets a little confusing.I have seen a few of the NYPD mobile command posts outfitted with a green strobe beacon on the roof.