No, a car’s brake lamps and police beacons are not within the range that would appear white, under any type of adaptation. You could stare at a brake lamp for 30 minutes and it would still look red. Even a low-pressure-sodium street lamp is going to keep looking orange after you’ve been standing under one for a long time. These are all more or less monochromatic light sources.
> Assume you just look at [the sun] up in the blue sky, using untinted eye protection.
Under ordinary circumstances if you look at the midday sun through a neutral density filter it will look white, though if your filter blocks out a high enough proportion of the light coming through it that might change. But in general, any light source will change apparent color if you put it through strong neutral density filter. Color doesn’t map 1:1 with normalized spectral power distribution.
Be careful to make sure that your filter also blocks solar radiation outside the visible spectrum. You can seriously damage your eyes looking at the sun through the wrong neutral density filter.
With adaptation, low-pressure-sodium street lamps look white to me. Key to this is having no other source of light as an alternative reference.
So if you are going to count adaptation, then all light sources are white. That makes the whole question of color completely pointless.
The same goes for not reducing the brightness. Burning out your eyes makes the question of color completely pointless. Here is a filter that would work: a small hole in a rapidly-spinning disk. Look right at the sky with the Sun, but with a duty cycle that reduces the light down to levels similar to typical indoor lighting. Another method, not quite as good due to field of view and imperfectly white screens, is the pinhole camera box commonly used to view eclipses.
No amount of adaptation brings low pressure sodium to white. Several hours doesn't achieve it. Half the cars under it will simply appear black, the rest yellow. You're left with little to no space for colour perception.
Illuminant metameric failure can happen with relatively normal LED and fluorescent lighting, particularly with a low color rendering index. You can get an orange object to appear black under the "white" lighting of RGB LEDs. Different orange objects would be differently affected depending on exactly what frequencies/wavelengths get absorbed. The objects could appear red, orange (good!), dark yellow, green, or black.
Under low pressure sodium, the eyes do adapt. Some cars are white, some cars are grey, and some cars are black. There is no yellow.
Eyes adapt, but mine get nowhere near the point of perceiving white items as looking anything but yellow under sodium. Always yellow near orange. 25 years of driving and dog walking in a very yellow world before LED started arriving. With all yellow snow when we still got snow. There was no white, until headlights caught something or dawn.
> Assume you just look at [the sun] up in the blue sky, using untinted eye protection.
Under ordinary circumstances if you look at the midday sun through a neutral density filter it will look white, though if your filter blocks out a high enough proportion of the light coming through it that might change. But in general, any light source will change apparent color if you put it through strong neutral density filter. Color doesn’t map 1:1 with normalized spectral power distribution.
Be careful to make sure that your filter also blocks solar radiation outside the visible spectrum. You can seriously damage your eyes looking at the sun through the wrong neutral density filter.