Every visible angle of a car has multiple lights on it so I don't think that's actually a double edged sword???
In my case, I frequently bump the light knob with my knee as I’m entering or exiting.
Black suffers from this somewhat, but less since backgrounds on the road are rarely black until the hour when headlights become essential. Muted grays are a handicap all day long in any form of suboptimal weather.
Something I think hinders visibility is also that cars are often amongst dozens of other lights, especially at intersections where it matters most.
But yes, I suspect if you were to redo that study in a country where people always have the lights on (perhaps due to local law if nothing else), you'd see the biggest difference in poor lightning conditions.