Borrow Some Color

You can grab colors (and more) from an existing Illustrator document without opening the file. From the Swatches palette (Window>Swatches), use the flyout menu and choose Open Swatch Library, then select Other Library. Then browse and find the document you want and click Open. A second Swatches palette will open with all the swatches from the other document. (One way to use this is to create for each client or project a document that contains only the swatches you use for that purpose, then load them as you need them.)