Cooking with Ornamental Cabbage (Kale)

Red cabbage is usually braised, not boiled. Following the instructions listed in your recipe, you're going to lose the flavor of the caraway as well.

For German-style sweet and sour red cabbage I typically saute some diced onion and apple in sugar and butter until just golden, add the shredded cabbage and then cook a little until the cabbage is glazed. Add some beef stock along with red wine vinegar, bay leaf and salt and then braise lightly covered until cabbage has softened. Sprinkle some flour over the top and add add'l beef stock and red wine to this. At the end, remove from heat and stir in a couple of tablespoons red currant jelly just to mix in and balance the sweet/sour flavors.

Are you trying to make Sauerkraut?

Either way for the pink colour you have a non-desirable bacteria growing. While most Sauerkraut has some of this, it is not always safe to eat. Time to throw it away?

If you salt cabbage, you need to ensure not too much salt is used (1% to 2% max), and make sure it is packed down very firmly, so only anaerobic bacteria will grow in any numbers

It doesn't need to be in a closed container, but it should have a firm fitting lid, without an air gap on the top

Also, once it goes past 20°C (70°F) you run the risk of getting other undesirable bacteria and yeasts, and general food rot