Garlic contains anthocyanins, water-soluble pigments that turn blue, green, or purple in a fermenting solution. While this color transformation tends to occur more often with immature garlic, it can differ among cloves within the same head of garlic. The garlic flavor remains unchanged, and it is totally edible without being harmful in any way. Fermenting makes the garlic more zesty and tangy but in recipes you won't notice a difference between fermented and regular garlic.
Fermented garlic is super bubbly. This is because garlic is a prebiotic, which is food for bacteria.