Place cranberry juice and jalapenos in a blender; cover and process until peppers are fully chopped. Strain through a double thickness of cheesecloth. Pour the strained juice into a Dutch oven; add vinegar. Stir in sugar. Bring to a full rolling boil, stirring constantly. Stir in pectin; return to a full rolling boil. Boil for 1 minute, stirring constantly. Remove from the heat; skim off foam. Add food coloring if desired. Carefully ladle hot mixture into hot sterilized half-pint jars, leaving 1/4-in. headspace. Wipe rims and adjust lids. Process for 5 minutes in a boiling-water canner. Yield: 8 half-pints.