As adding a style to a field changes the whole field, what you can do is create a new Label field just before field you using and and add the style Red to it. You may need to do move the old field over a little bit. It will more look like " * Workorder" but as you can't have 2 color labels.
Else, you can have two label fields and then a field the user enters the data in like
<Label><asterisk><imput field"
Longtext * _________