Let’s start our trip at http://www.apple.com/support/ On that page, you’ll find a blue header for iPod support (I’ve copied it here for you). Notice how it has the slightest bit of shading to it that makes it look just a bit more solid than if it was just a plain shade of blue. Here’s a re-created graphic for comparison. The difference you see is the power of gradients.

Now, let’s say you want to create the same look yourself. No need to try to figure out what color blues to pick, just use your color picker! First, draw a shape and for it’s fill, choose Gradient Fill. If you’re using the Black theme, you’ll end up with something like the shape on the left. It really doesn’t matter what it looks like exactly, because we’re going to be changing it. Right now, your gradient fill indicator is going to look a little like this. What you want to do is get the colors from that bar above into the color wells. You’ll do this by first clicking the color well on the top which will open the color picker. Once it’s open, click on the little magnifying glass on the left. This will turn your cursor into a magnifying glass and enable you to pick up any color you hover over with a click. Mouse up until the center point inside the glass is as far up in the blue as you can go before you get to the outline. When you click, the color in the color well will be replaced with what you just clicked on (my result is to the right, yours may vary). After all that, I’m sure you can figure out what comes next! That’s right, boys and girls, repeat the steps using the bottom color well and click on the bottom most shade of blue in the bar. If you do it JUST right, you’ll end up with a color bar that looks like this. Notice how that hint of color difference makes it look like there’s a light coming from above and a darker surface below. IT POPS RIGHT OUT AT YOU!