Cooking recipes:

When selecting garlic, it should be big, plump and firm, tight silky skins with its paper-like covering intact, not spongy, soft, or shriveled. Why buy small ones that are a pain to peel? As with all ingredients for cooking, buy the best garlic you can afford. Also remember that a single bulb of garlic usually contains between ten and twenty individual cloves of garlic. The individual cloves are covered with a fine pinkish/purple skin, and the head of cloves is then covered with white papery outer skin. When preparing garlic for cooking, remove any green sprouts from the center of the garlic clove, as the sprouts add an unpleasant bitterness.
Storing Garlic
Unbroken garlic bulbs will keep for up to 3 to 4 months. Individual cloves will keep from 5 to 10 days. Store in a cool, dark, and dry location (dampness is the enemy of garlic, so store away from stove and sink). If the cloves sprout, the garlic is still usable and the sprouts can be used for salads. Garlic is known to contain sulfur compounds which can react with minute traces of copper to form copper sulfate, a blue or blue-green compound. The amount of copper needed for this reaction is very small and is frequently found in normal water supplies. Raw garlic contains an enzyme that if not inactivated by heating reacts with sulfur (in the garlic) and copper (from water or utensils) to form blue copper sulfate. The garlic is still safe to eat.
If fresh garlic is picked before it is fully mature and hasn't been properly dried, it can turn and iridescent blue or green color when in the presence of an acid. It may be caused by an allinin derivative. A reaction between garlic's natural sulfur content and any copper in your water supply, or in the cooking utensils you are using (such as cast iron, tin, or aluminum) can sometimes change the color of garlic. The other sources of copper might be butter, lemon juice, or vinegar.
Garlic will also turn green (develop chlorophyll) if exposed to a temperature change or is exposed to sunlight. Some people say it can be stored for 32 days at or above 70 - 80° F to prevent greening (but I'm not yet sure that is true). Are you using table salt instead of kosher or canning salt? That can cause the garlic to turn blue or green. Table salt contains iodine, which discolors whatever you're pickling. Use kosher or pickling salt. Different varieties or growing conditions can actually produce garlic with an excess natural bluish/green pigmentation (anthocyanins*) made more visible after pickling.