For an image available online, the link falguni1 gave is real useful. If you have that image saved on your computer, use GIMP [gimp.org] to pick the color of the exact specific area. Also if you are using the latest Internet Explorer 8 beta 2 with Developer Toolbar installed, it has a nice color picker to use pick colors from web pages. Open IE8, [if only you have Developer Toolbar installed], hit F12, and go to Tools menu. [see image attached.]
Firefox also has an add-on called Colorzilla that will give you the hex and RGB values for any pixel.