Customers find the salt has a great taste and is not overly salty. Also known as Sel gris. 
Celtic salt or Celtic sea salt, also commonly known as sel gris (gray salt) in French, is harvested from seawater in the estuaries near the town of Guérande in France. Sel gris is a coarse salt that is typically harvested with a moisture content of 15%, whereas most sea salts and commercially manufactured salt maintain moisture contents of less than 1%.As the tide comes in, seawater is first allowed to settle in clay silt ponds where the combined effects of wind and sun form a dense brine. The brine is then channeled to shallow salt pans dug in the native clay where it crystallizes via solar evaporation to form salt crystals. The clay from the silt as well as from the salt pans impart sel gris with its characteristic gray color. (Content from https://thepaleodiet.com/what-is-celtic-sea-salt/).