In your CP, scroll down to Replacement Vars - select Add. In the "Code to find" box, enter <blacktext>, and in the "Code to insert" box, enter <font color="#000000">. Select Add again, and insert </blacktext> and </font> in the appropriate boxes, and you'll be able to use <blacktext> and </blacktext> in every template. This can be done with any color.
Hope this helps

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-jim