More than likely, I suspect this is an agreement between NHTSA and VW, to put an end to the claims of misfueling with gasoline in a diesel and wrecking the HPFP.... Not that VW had a leg to stand on in the first place about misfueling causes in the first place.... if this truly was as pervasive a problem as Vw claims for wrecking HPFP's, VW would have immediately been installing these on all diesels starting back in 2009.
I am of the opinion that yellow is the standard color for diesel fuel in the USA if stored in tanks, and that VW should mandate that all TDI's get a bright yellow fuel cap that says "Diesel Fuel Only". Stickers can fall off, peel off, fail, what ever, but a cap is on the car for good, for the life of the car.