Vegetables always brilliant
To remedy this that cooking the vegetables become grayish and unattractive, you have to shorten the cooking time as possible:
a few minutes to spinach and herbs
Green beans and asparagus for 7-8 minutes are enough to remove the raw without interfering too much with the organoleptic qualities (color, flavor) vegetables.
Do not put the lid on pots and, when ready, raised vegetables and mash in a bowl of cold water and ice: thermal shock keep them shiny and firm.