This is more of an FYI than anything else...
I'm prototyping my workspace, and I have a habit of giving UI elements such as charts distrinct background colors during prototyping until I get things laid out the way I like.
I had done this with an XYGraph with bar series data.
I could not figure out for the life of me why my graph would show the the xpath data fine, and would show the ypath tick marks with the correct range, but would not render the actual bars.
Once I removed the background property on the XYChart object, the bars appeared.