A Ticking Time Bomb In My Pantry

My first attempt at making sauerkraut was a complete failure.  My second attempt at making sauerkraut was a success. I ate most of it myself and gave some away but it is all gone. So this time I thought I would try it again with a red cabbage.  I used the same recipe except no kohlrabi this time and a red cabbage instead of a green cabbage. The red cabbage was bigger than the green and it filled up my glass flip top container to the top. I took a couple cups of red cabbage back out before I put it in the pantry and covered it with a towel. I peeked the next day and saw the towel was blue. Hold the phone.  That towel with owls on it was white. How did it turn blue? I see the cabbage was fermenting much faster than the first batch. I opened the lid. Bright magenta fluid spewed out all over everything.  I rush the red mess to the kitchen sink. I clean up the red stains as best I can. I set the mixture back in a deeper bowl this time and cover it up with an older kitchen towel. I have washed that kitchen towel twice now but I still see a blue stain. During the last batch of fermenting sauerkraut I opened the lid once a week.  This batch I open the lid every day to burp the sauerkraut and I put it in the kitchen sink before I open the lid. I do not need to be stained twice to learn my lesson. Every day now I open my pantry door with trepidation. I am afraid my kitchen towel will turn blue! How can a red cabbage stain blue?  Isn't red a primary color? This batch of sauerkraut, if it turns out to be edible, is going to work some powerful fermentation magic on my belly!