I believe that food processing by products in the USA are still classed as waste streams and cannot be used for human consumption.
Vegemite is manufactured from the yeast extract produced as a waste stream by the beer fermentation industry. Vegemite was banned for sale in the USA for a long time, and this ban may well be still in place.
I have some experience with the Vegemite process in Oz and included in the process is a caramelisation step which effectively gives Vegemite it's dark color. Yeast extract is a kind of "poo" color and was thought to be a poor choice of hue to market (strange, because one can argue that chocolate is also excrement color, but is laden with sugar and caffeine and flavor, so we may as consumers let that go to the keeper)
Ironically in the USA, the way the FDA laws are structured, if a beer manufacturer said they were fermenting their barley malt, to produce yeast extract at the bottom of their vats and that was their product goal, then the alcoholic beer in the vats would be a waste by product and banned for sale to humans for consumption