Ok, so yellow headlights are legal for a manufacturer or importer un fmvss 108 table 1A, but it is true that state laws still apply. I was operating under the impression that federal law supercedes state law in this case.
So it *does* varh state to state.
That being said, OP, if its legal in your state, its a legitimate option for reducing backscatter at night and with dust or moisture in the air.
And, as others are pointing out, given the number of idjits rolling around unharassed with downright blue, pink and green headlights, Ive personally seen blue turnsignals, and smoked/fogged headlamps and taillights, it might still be an option for you to explore. The nice thing about a vehicle with a glass headlight lens is that its removal if you do get a ticket fo it, is just a shot of paint thinner away.
OP, Ill see if its legal in your state. If I can find th applicable law, ill post it up for you.
Oregon
https://www.oregonlegislature.gov/bills_laws/ors/ors816.html
816.050 Headlights, rules. [Is very close to the top]
...
3. Headlights shall show a white light described in Standard number 108 of the Federal Motor Vehicle Safety Standards.
So that appears to say its white light only for headlamps, however fmvss108 table 1a states white or yellow.