Select a letter in the color you wish to duplicate. PRess Ctrl+D to open the Font dialogue, then click on the color button and in the ensuing dropdown, select More Colors at bottom. In this next dialogue, select the Custom tab, and a readout of RGB will be below the color graph.

In newer version of Word, once you have opened the Custom tab and clicked OK, the custom color will show up below the standard colors in the color dropdown until you close Word.

Best,
Ulodesk