How does blanching vegetables help preserve their color?

Blanching briefly stops enzyme activity in vegetables. Enzymes like chlorophyllase and peroxidase naturally break down pigments such as chlorophyll, carotenoids, and anthocyanins over time, causing vegetables to turn dull, brown, or yellow. The short exposure to boiling water deactivates these enzymes, halting that degradation process. For green vegetables specifically, the heat also drives out air trapped between cells, which makes the green color appear more vivid immediately after blanching. The quick cold-water bath that follows stops the cooking process before heat itself can break down the chlorophyll. This combination of enzyme deactivation and rapid cooling is why blanched and frozen vegetables retain their bright color far longer than unblanched ones.