You can make the letters any color you want before creating an outline around them. Just highlight the word or phrase, and then select a color from the “Font” panel at the top of Word.
If you don’t see this icon, click the Home tab at the top of Word.
If you go too thick, you might make the text unreadable. You can always undo the last action in word by pressing Control + Z (PC) or Command + Z (Mac).