Avoid kale that is limp, wilting, bruised, or discolored. Curly kale, the most popular kind sold in U.S. supermarkets, is usually green, but sometimes is blue.
Tuscan kale has deep green, almost black leaves.
Flowering kale comes in a variety of pastel colors, usually shades of yellow and green. Because kale deteriorates quickly in warm areas, look for it stored on ice in a chilled section of the produce department, or at an outdoor winter market. James Peterson, author of Vegetables, warns that unless kale is very young, it is tough and requires cooking for at least 20 minutes. He suggests blanching the greens before cooking to help tenderize the leaves. However, if you're serving kale in a soup or stew, there's no need for this extra step.