In this hour, you looked at working with color. Variations make simple, "by eye" adjustments, letting you choose from differently enhanced thumbnails. Levels and curves apply adjustments more scientifically. You now know how to make the sky a perfect blue and the grass a greener green. You know that adjusting levels lets you set limits for dark, middle, and light tones in an image. You have learned about color balance and how to apply changes to hue and saturation. You have seen how to change the brightness and contrast of an image.
Color adjustment is one of Photoshop's most-used features, and one that you'll rely on whenever you need to touch up a photo or a scanned image. Practice with it as much as you can, using your own favorite images.