Why is Himalayan Salt Pink?
As stated in the Wikipedia article about the salt, the pink color that sometimes occurs is due to iron oxide:


  Himalayan salt is predominantly sodium chloride (95-98%), contaminated with 2–3% polyhalite and small amounts of ten other minerals. The pink color is due to the presence of iron oxide.


As a source, the article references this page on HowStuffWorks.com. It gives a slightly broader list of chemicals that cause the color differences:


  Some pink salts, such as the salt harvested in the Himalayas, get their color from calcium, magnesium, potassium, copper and iron, Others contain carotene from salt-tolerant algae and are more peach-colored.