I don't like these blue headlights! They produce too much glare and it's harder for me to see when these vehicles are approaching. This is a typical and frequent comment made to me in discussions.
There are two types of headlights that emit blue coloured light, one legal and one not.
The legal type is called a Gaseous Discharge Headlamp that works by passing an electrical current through a gas, much like a neon sign. The light from these lamps tends to have a slightly blue or purple cast to it due to the colour temperature of the light. They have a more comfortable light for the driver and a wider beam pattern that can spread more light to the road edges and thus provide safety benefits.
These lights meet the technical definition of white light and meet the same standards for glare that conventional headlights do. Perhaps we notice them more because they are still relatively new and different from common headlight systems. If they are kept clean and correctly aimed they will perform properly without excess glare.
The illegal type is a conventional filament bulb that has the glass coated with a substance that appears gold coloured when the light is turned off. This coating removes colours other than blue from the light emitted by the bulb so that the light they cast appears blue-green when observed by the driver. These lights are dangerous as they provide lower levels of illumination and if high wattage bulbs are fitted to overcome this, more glare for approaching drivers.
An associated problem occurs when one buys a gaseous discharge bulb kit and installs it in a conventional bulb lens assembly. The lens is not designed to properly focus this light source and so results in more glare for oncoming traffic. This retrofit is illegal.