How do you keep green vegetables green when cooking them?

To keep vegetables bright green, cook them briefly. When blanching them, use a large amount of boiling water and keep the lid off. Cook the vegetables only until tender-crisp or tender and bright green (about 30 seconds or up to six minutes), then plunge the vegetables in ice water to stop the cooking. The ample water and lack of a lid dilutes acids in the vegetables (or the water) and allows the acids to escape the liquid, keeping acid from discolouring the chlorophyll. It also helps to salt the cooking liquid, which partially prevents chlorophyll's conversion to a drab greyish green. When blanched like this, vegetables can be chilled then fully cooked at a later time yet still retain their bright green colour. While alkali (bicarb soda) will convert chlorophyll to bright green chlorophyllin, it destroys the vegetable's texture and its vitamins.