Does the yellow tint really help with seeing better, or is it more of a looks thing....it's France where it's been used most, right?
FWIU (MrPink feel free to jump in and correct me if I'm wrong) It's probably a little bit of both in this situation.
Coating lenses (or bulbs) like this in any color will decrease output slightly, but yellow colored light is easy/quick for the human eye to process and use especially in the dark. IMO there is a definite benefit to "selective yellow" headlamps and/or fogs especially in bad weather, although be careful if your local police are sticklers for lighting. Here in the states selective yellow is allowed in fog lights, but headlights are supposed to be "white."
And yeah, selective yellow lights were used in France for a long time.
https://en.wikipedia.org/wiki/Selective_yellow