Unfortunately, there's no setting or option for this.
You could save the image with a black background and then use an image editing program to make it inverse.
Or use the "Layered Screenshot" option to save the background, bodies, labels, and UI all as separate layers which would make just inverting the label colors quite easy.
Click the Camera icon in the lower left, then click "Layered Screenshot".
Click the Camera icon agian, then the folder icon to open the folder where the individual layers were saved.