First, welcome to herb gardening!

Sage is not a cool weather plant, thought it does prefer drier conditions than you probably have (same with rosemary, thyme, and oregano). I'm in Denver, CO, so hot and dry right now and my sage is happy happy. I would imagine that it's the humidity and drainage that is causing your sage leaves to blacken. Also realize that sage is basically a shrub and does like to have room, so if it's in a smaller pot, it won't be happy. You could try a larger pot, with some sand mixed into the soil to provide for better drainage (and some rocks in the bottom), as well as making sure it can breathe--don't stick it back in the corner, but make sure it has some airflow.

You can try the cilantro and parsley indoors, if they will get enough sun. Cilantro will bolt (produce the flower stems) when it gets hot, or is just ready--cutting the leaves prevents the bolting. Parsley is biennial--it generally doesn't produce it's flowers until its second year, though occasionally it will the first year if it gets really hot.