Salt colors differ in different places

The color of pure salt (sodium chloride) is white but it may have different colors depending on where it is made. Roast bamboo salt we see in Korea is grey while salt made in Hawaii is black as it is mixed with black sand that is common in volcano areas. In Dakar, the capital of Senegal, there is a saline lake called Lake Retba and the salt there has pink color. The color was made when red algae meet white salt crystals, blending with each other. When mix with green algae, the color then changes to green.

Sometimes salt can be colored even without foreign materials. If sodium is replaced by electron between the crystal structure of sodium ion and chlorine ion, the color changes to blue. If sodium is replaced by iron ion, the salt becomes red.