I have seen white teflon pipe thread tape used on gas lines and called it out. In the past I always understood that the white was for water lines as it was thinner and the yellow was for gas as it was thicker and less likely to tear.
After doing research several manufacturers are selling the same thickness tape in various colors with some manufacturers producing white being rated for gas.
My question is does the plumbing code require any thread tape used on gas lines to be yellow? I could not find any info on the subject.