I've come across a weird "artifact" that can be triggered when plotting labels with `outline=True`: ```python sdata.pl.render_labels(outline=False).pl.show() ```  ```python sdata.pl.render_labels(outline=True).pl.show() ```  It's a little hard to see, but in the 2nd figure, there appears to be some kind of "shade" in the top-left corner of the plot. I went digging a bit for possible causes -- please see the PR linked below for a potential fix.