Brightness/Lightness/Luminosity
The only things missing from our color wheel are the different brightness levels for all those colors. You could create a 3D color wheel in the shape of a cylinder with dark colors at its base and the brightest colors at the top (Figure 10.3). But because we'll probably never see anything that fancy in Photoshop, we'll just describe the brightness of a color using one of three words: brightness, lightness, and luminosity. Each of those words is just a slightly different way to describe how bright a color is, and as you become more traveled in Photoshop, you'll notice that Adobe can never seem to make up its mind on which one to use. So don't let all the terms confuse you, because they basically mean the same thing.
Figure 10.3. A three-dimensional color wheel would have dark colors at the bottom and bright colors at the top.
Every color you've ever seen in Photoshop can be described as a combination of hue, saturation, and brightness (HSB). You'll find me referring to that term every once in a while. The adjustments we'll be doing will end up shifting the colors in our image based on that color wheel. Most of what we do will result in either moving a color around the wheel to change its hue or shifting it toward another color by pushing it to the opposite side of the wheel. Now that you have a general idea of how to think about a color wheel, let's jump in and see how we can mess with the colors in our images. So, crack your knuckles and push up your shirtsleeves, cause we're ready to start mousing around. We'll warm up with my favorite method for manipulating color.