California vehicle code (VEH 25251.5.7(a)) has an interesting inclusion of strobing yellow center light proportional to brake force.

https://leginfo.legislature.ca.gov/faces/codes_displaySectio....

What I think is absurd is red, yellow, and/or blue flashing lights except for emergency vehicles on or conveying to an emergency. Throughout the South US, maintenance vehicles flash zillions of lights creating visual distractions and flasher fatigue.