There are a number of reasons that pickles may turn dark. They include using water with too many minerals, especially iron. Using a very dilute vinegar solution. There should be at least one part of vinegar to every 3 parts of water. Recipes that don't use this ratio are unsafe. Using too many ground spices. Cooking too long with spices or packing the ground spices into the jar. Using cucumbers with a low nitrogen content. Development of corrosion on the underside of metal lids. Using iodized salt, or iron, brass or copper utensils in preparation of pickles. Pickles prepared in these utensils should not be eaten. If your pickle liquid turns pink shortly after canning, this may have been caused by use of over-mature dill. Use of sunburned or over-mature cucumbers may produce a product that is dull or faded in appearance. Pickles that have small brown spots have been held too long before pickling. To avoid dark pickles, use only unchipped enamel, stainless steel, or heat-resistant glassware when heating pickles, or try a stone or crock jar or a heavy plastic container. http://www.ext.nodak.edu/extnews/askext/pickrels/4662.htm