Answer:
Some veggies will "fade" in color when boiled or roasted. The boiling process contrubutes several factor that could effect color such as ph of the water and oxidation of in no doubt acids in foods. The methods of cooking which are perform at a higher warmth will change the horizontal of pH more drastically, because the denaturization of the proteins will be increased. Most likely, as the heat rises, the pH will lower, and the lower the level of pH, or the better the acidity, the more the pigment will lose its raw color.
The best way to cook fresh veggies so as not to effect color would be to steam them. I do it surrounded by the microwave which used the least amount of wet possible. I always own brightly colored veggies with this method.
What vegetables are you talking going on for specifically? I've never seen it transpire. All the veggies I've cooked stay the same color after cooking as they be before. Carrots stay red, corn stays yellow, broccoli, spinach, green beans, Brussels sprouts, cabbage adjectives stay green, cauliflower stays white. Zucchini stays green or yellow, depending on the type. I've never see a vegetable change color, so I'm interested surrounded by what you're cooking and how you're cooking it.
Please expand on your question next to more info.
The chief reason is that they are over cooked.
The purple vegetables (red onions and purple cabbage) tend to change and become lighter almost a blue color as they cook. Although the skin of an eggplant tend to stay that deep aubergine color.
The root they cange is that the compound (anthocyanin) that gives the cabbage the red / purple color react with alkaline substances. Tap marine is often full of alkaline minerals such as lime. Sometimes tallying about 1 teaspoon of caustic agent, such as lemon juice, vinegar, or wine, to the pot when using hit water to cook your red / purple cabbage may bring subsidise the original color.
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