I do two things to keep cilantro, coriander leaves and Italian parsley looking green and almost alive when I have a surpluss of them.
1. I process the clean, dry leaves with either X-tra virgin olive oil; if that is what suits your use or any other oil (without taste like grapeseed, etc..). Always keep the leaves covered with enough oil and refrigerate...Yes... refrigerate, although the oil will cloud, it will behave when at room temperature without any change in flavor.
2. If I want to use it for guacamole or as part of a sauce that is no big deal, since it is not the "piece de resistance", I divide the bunch, depending upon the size, layer it between paper towels and microwave for 15 seconds in high. This will kill one of the enzymes that makes them turn dark. Then after they refresh, I pack them in freezer bags, take out as much air as possible and freeze, it will probably last about 2 months.
I know that because Once I went on vacation and when I returned home, it helped me whip up a sauce in no time for a hungry family.
"Cooking is like love...enter it with abandon or not at all"