Picture three markets in a row, named by colour. The white market is the maker's own approved sellers. The black market is where things that are illegal to sell change hands. Between them sits a grey one: everything in it is real and selling it breaks no law, yet it runs along a route nobody official chose — stock brought in from elsewhere, bought up in bulk, resold when supply runs short. Grey is the colour of that in-between space, and every use of the phrase points back to it.