In a non-reactive container, combine the cabbage, peppers and onions. Sprinkle with salt and toss to combine. Cover and refrigerate overnight.
Remove cabbage mixture from refrigerator and drain, discarding liquid. Rinse cabbage mixture with cold water and drain again. Transfer cabbage to a large saucepan. Place spices in a square of cheesecloth and tie with kitchen twine. Add sachet to cabbage mixture. Combine vinegar and sugar in a liquid measuring cup. Pour over cabbage mixture and stir to combine. Bring to a boil. Reduce heat to simmer, and cook, stirring occasionally, for 20 minutes. Remove and discard sachet.
Ladle relish into jars. Cool on a rack to room temperature. Cover and refrigerate for up to 2 weeks.
(c)2004 Martha Stewart Living Omnimedia, Inc. All Rights Reserved.