Yes, but for the virtual tag to turn on a different color, when there is a any text (irrespective of whether its a weblink or plain text).
So you mean a colour different from other tags?
Not it changing colours depending on it's content?
Then you could simply use something like:
{color: 200,0,0}$IsNull(<Comment>,,<Comment>)
If <comment> is empty it won't show at all, if <comment> has a value it will display. (in red in this case)
edit:
The values are r,g,b (red green blue) you can use any value from 0 to 255.
255,255,255 is white
You can also set font type, font size, contrast. A forum search should show some examples.