When vegetables take a sad turn from bright green to khaki drab, it conjures memories of grade-school cafeteria food and the ruined texture of canned asparagus. The most common culprits: overcooking and acidic dressings. A cook has to know how to care for the delicate source of the green: chlorophyll.
Vegetables such as green beans, broccoli, and asparagus lose their bright color—and crisp texture, for that matter—after six or seven minutes of cooking. If you know you'll be eating them immediately, just remove, drain, and serve. But if you'll be busy assembling other dishes, consider blanching and shocking. Cook for two minutes in salted boiling water, then remove vegetables immediately and plunge into ice water. The ice back halts the cooking process and helps set the color. Later, the chilled vegetables can be quickly reheated—by sautéing in a bit of olive oil, for instance—without losing their green.
But blanching won't keep veggies vibrant if you dress them too soon with an acid such as vinegar or lemon juice. Wait until just before serving (as we do with our SuperFast asparagus sides).