Combine cabbage, green tomatoes, onions, red and green peppers and salt in a large glass or stainless steel bowl. Cover and let stand in a cool place for 12 hours or overnight. Transfer to a colander placed over a sink and drain. Rinse with cool water and drain thoroughly. Using your hands, squeeze out excess liquid. Set aside.
Prepare boiling water canner. Heat jars and lids in simmering water until ready for use. Do not boil. Set bands aside. Tie pickling spice, gingerroot and mustard seeds in a square of cheesecloth creating a spice bag. Combine drained cabbage mixture, vinegar, water, sugar, turmeric and spice bag in a large stainless steel saucepan. Cover and bring to a boil over medium-high heat. Uncover and boil for 5 minutes, stirring frequently. Reduce heat and boil gently, stirring frequently, for 1 hour, until thickened to the consistency of a thin commercial relish, about 20 minutes. Discard spice bag.
Ladle hot relish into hot jars leaving 1/2 inch headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot relish. Wipe rim. Center lid on jar. Apply band until fit is fingertip tight. Process jars in a boiling water canner for 10 minutes, adjusting for altitude. Remove jars and cool. Check lids for seal after 24 hours. Lid should not flex up and down when center is pressed. Makes about 6 to 7 (8 oz.) half pints.