Wash and pit cherries. Drain before measuring. Dissolve alum and salt in 2 quarts cold water. Add cherries. Let stand about 6 hours. (If cherries float, cover with plate weighed down with a jar filled with water.) Drain and rinse cherries. Add sugar to 2 cups fresh water; cook until sugar dissolves. Add cherries; boil 2 minutes. Remove from heat. Add food color and extract. Let stand in a cool place 18 to 24 hours. Return to heat and boil another 2 minutes. Pour, boiling hot, into hot jars. Adjust lids, and process in boiling water bath or steam canner for about 5 minutes at sea level (add one minute for each 1000 feet above sea level), to assure sterile seal.