keeping greens green:

Peas, broccoli, spinach--they can all turn less-than-appetizing pukish green colors during cooking.  This is necessary with casseroles and such, but it can be avoided in other instances.  One way to maintain their color is to add them toward the end of the cooking process.  To cook them more thoroughly, one can blanch them, which means to dip them in boiling water and then remove and then add to a dish toward the end.