Yellow, like the DTOM flags?
I don’t think there really is a libertarian flag/color.
Yes, the color is gold.
http://www.vforvoluntary.com/wiki/VoluntaryistSymbolism#Anarcho-capitalist%20flag
According to the quote in your post, wouldn’t it be gold AND black?
Well libertarianism doesn’t necessarily imply gold…maybe anarchism…depends.