How can I match colors on my blog?

Let me preface this "mini-tutorial" with some background. I've had Photoshop for years, just started to use it for anything more than re-sizing pictures in the last year and everything I know about Photoshop I've googled. Since I only learn what I need to know, it came as a total surprise a few months back to discover the purpose of the eye dropper tool. Simple but so useful to a bloggers. Get this...you can open an image, click the eyedropper icon in your tools, click anywhere on the image you want to discover the its color and voila, the color code appears like magic! Believe it or not when previously designing banners or latching titles for the site I would "eyeball" it, but no longer. Imagine that.