Used to be in Ontario, Canada that the blue lights were only for Snow Plows. It was comforting to see that small blue flashing light up ahead as it meant the road was freshly plowed and if you kept the light in view you were usually not going to run off the road.
Not sure what they use now.
At the moment the plows still run with flashing blue.
Police are switching to a combination of blue and red lights.
http://www.e-laws.gov.on.ca/html/statutes/english/elaws_statutes_90h08_e.htmFlashing blue light on snow-removal equipment
(31) No person shall, while operating a road service vehicle on a highway, plow, salt or de-ice the highway or apply chemicals or abrasives to the highway for snow or ice control unless the road service vehicle is equipped with a lamp producing intermittent flashes of blue light visible for a distance of 150 metres from all directions. 1996, c. 33, s. 11.
Restriction on use of flashing blue light
(32) No person shall operate a lamp that produces intermittent flashes of blue light on a highway except,
(a) a person operating a road service vehicle in the circumstances described in subsection (31); or
(b) a person operating a police department vehicle, together with a lamp that produces intermittent flashes of red light, as permitted by subsection (14.1). 2007, c. 13, s. 17 (8).
Red and blue lights to the front restricted
(14.1) In addition to the lighting requirements in this Part, a police department vehicle may carry lamps that cast red and blue lights, but no other motor vehicle shall carry any lamp that casts red and blue lights to the front. 2007, c. 13, s. 17 (2).