AFAIK, most of the actually 'blue' headlights are not street legal. A Product of cheap aftermarket "HID Kits" or cheap XENON bulbs. Also, at least in Texas, basically any modification to your OEM headlights is verboten.
I heard before that we perceive slightly yellow light as white (because of the sun) and these 'blue' lights are really pure white but our perception shifts it.