Grey has almost no pigment history, because for most purposes nobody made it. It was mixed, or it was what a material happened to be.
In painting, grey is black and white, or a neutral obtained by mixing complementaries, and the interesting grey pigments are few. The technique that matters is grisaille, painting entirely in greys to imitate carved stone, used on the outer wings of altarpieces so that a closed altarpiece appeared to be sculpture and an opened one broke into colour. That is a use of grey as the absence of an event rather than as a colour in its own right.
In cloth, grey was undyed wool. Sheep are not white; fleece runs from cream through grey to brown to black, and cloth made without dyeing at all is some version of grey. That made it the cheapest cloth there was, and European sumptuary regulation and monastic rule both used undyed cloth to mark the renunciation of display. The greyfriars took their name from it. So, from the other direction, did the greycoats of the poor.
The nineteenth and twentieth centuries gave grey a second meaning, as the colour of industry, of the city, of the uniform and of the office, and then a third as the colour of neutrality, of the middle position and of the undecided. None of these has any depth of tradition behind it.
Grey is the clearest example in the palette of a colour whose meanings come from economics and from materials rather than from any symbolic scheme.