One more important point that I forgot to share. If you attempt to fix the same underlining glitch I experienced by completing my above-listed steps, you may discover, if you haven't already, all of your text will be formatted in underlining when you create a new message. There is another fix to avoid this potential annoyance.
When you are selecting your Underline Style, be sure to:
1. Select "None" for Underline Style.
2. The rest of my instructions work correctly.
The mistake I made was, when I looked at the "Underline Style" box, it was empty (blank with nothing selected). So I assumed (uh-oh!) that this meant I had to change the style and select one of the underline type options. The truth is, I did not need to select anyting except "None." "None," as strange as it seems, was indeed actually selecting an "Underline Style."
Simply put, the Underline Style box cannot be empty; otherwise, you will not see your format option of underlining selected text (although for some reason you can see it in "Sent Mail"). And if you select one of the underline types (single line, double, etc.) ALL of your text will be underlined. Lesson learned. (Also, when you select your color, your underline color will automatically match; therefore, there is no need to select an underline color unless you specifically choose to have a different color underline than the font color.)