What Makes Bread Gray?
What kind of salt are you using?

In the presence of iodine, starch can turn a surprisingly purplish-black color. This phenomenon has be leveraged for many decades in medical examiners' offices, to help determine the contents of a last meal in a cadaver (pardon the unappetizing digression).

Iodine is an essential nutrient, vital for the proper functioning of our thyroid (read more about Iodine Deficiency) that has relatively few ways of entering our bodies through our diet other than through shellfish, meats, eggs, and some dairy products. 

One way to combat the problems of iodine deficiency is its addition to our salt, which we consume in predictable quantities and never goes bad. Table salt contains up to 25mg/kg of iodine and that number has been on the rise since its safety and helpfulness have been demonstrated repeatedly. Sea salt contains some iodine, as it is naturally occurring in the ocean, but in a much smaller quantity.

Maybe when you were at the beach, your salt supply changed to sea salt or an uniodized version and and when you returned and used the regular Iodized Morton's or Iodized sea salt.