Uh...how do I make this line black?

What you have is normal for a single stave. Initial barlines are usually only shown for multiple instruments or for instruments that use more than one stave (e.g. piano). The idea is to "tie" the staves together to show that the are all one system and that is not needed for single staves. So, if you want your score to follow standard notation practice, leave it alone. If you really want that initial barline you can have one by ticking the "barline at the start of single stave" box in [Format]>[Style]>[Barlines].