Ever assume a gentle bubble meant better fermentation? I was all about that low and slow life until I saw your beet kvass art project. This proves a wild ferment can be more protective, so maybe my cautious ways need an update.
Got a similar mess with sauerkraut once. Beet juice stains are brutal, might need a primer coat over that magenta. Vigorous ferment means happy bacteria, at least. Leave more room in the jar next time to prevent geysers.