In this thread I asked a question about rendering inverted pattern images via image draw modes (which doesn't work). Another approach I tried was to invert the image being passed to setPattern.
However, I've found that neither setting the inverted flag on the image via setInverted(true), nor creating a new inverted image via invertedImage() has any effect on the rendered pattern. I'm assuming that both approaches just set a flag on the image (rather than the latter actually producing an image with inverted values), and that setPattern disregards that flag.
The docs specifically mention that inverted images work when set as stencils. I assume that they should work when set as patterns as well.
) Filed that, will fix asap!