If your cranberry bread turned green, it's likely due to a reaction between the acidic cranberries and the alkaline baking soda. Cranberries contain anthocyanins, which can change color when exposed to different pH levels. When too much baking soda is used, or the cranberries are overly chopped or bruised, the pigments can shift to a blue-green hue. To avoid this, use the right amount of baking soda and gently fold in the cranberries.