In order to retain the colour of vegetables before freezing, they should be

In order to retain the color of vegetables before freezing, they should be "blanched." Blanched means that the vegetables are briefly boiled in water or steamed and then immediately cooled in ice water. This process stops the cooking process and helps to retain the color, flavor, and nutrients of the vegetables. When vegetables are frozen without being blanched, they can become discolored and lose some of their flavor and nutrients. Blanching is a simple and effective way to preserve the quality of vegetables before freezing.