Red choy is a specialty variety of bok choy. It is related to cabbages, broccoli, and brussels sprouts. The red coloring of the leaves is due to anthocyanins, a beneficial flavonoid that causes the purple, red, or blue pigmentation in plants. As the color might indicate, the flavor of red choy has a sharper bite than other bok choy varieties, though over all the flavor is still quite mild.
The entire plant is edible. You can separate the leaves by cutting off the base of the plant. Rinse thoroughly, as dirt can become stuck in the cracks between the leaves. Use your red choy as you would any other bok choy. It is perfect for a stir-fry, sautéed lightly in oil, or steamed. You can use your red choy as a substitute for cabbage or mustard greens. The leaves are tender enough to use in a green salad.
As is the case with all greens, be sure the red choy is dry before stored in a plastic bag. Either wait to wash until you are ready to use it, or use a salad spinner to dry the leaves, then store with a paper towel in a plastic bag for four days to a week.