We purchase our red cabbage in either supermarkets or farm stores (when in season), and we always look for firm heads without discoloration or imperfections. Red cabbage adds color to salads and cooked recipes. Red cabbage leaves are colored dark red/purple. However, the plant changes its color according to the pH value of the soil that it is growing in, due to a pigment called anthocyanin. In acidic soils, the leaves grow more reddish, while an alkaline soil they will produce rather greenish-yellow colored cabbages. This explains the fact that the very same plant is known by different colors in various regions. When we were children we used the juice of red cabbage as a home-made pH indicator, turning red in acid and light greenish-blue in basic solutions. On cooking, red cabbage will normally turn blue. To retain the red color it is necessary to add vinegar or acidic fruit to the pot. See the nutritional charts for raw and cooked red cabbage.