I almost exclusively use black templates to help prevent eye strain, and this feature would be incredibly helpful! It is quite irritating to have to highlight something multiple times for it to somewhat stand out, and even then, it's not as fluorescent as I would like! It would also be helpful because I like to coordinate the importance of the highlighted term with the strength of the highlighter.

Yes! I came here wanting to post this as well :-) I'm a storyboard artist, I've made a nice pdf template and I'm enjoying drawing stuff using the pen tool, would be great to be able to mark shadow areas with the highlighter (it's really useful that it draws *behind the lines*, kind of makes up for the lack of layers!), but sadly the low opacity makes it look terrible when you try to fill an area in with several strokes. I'd love to be able to turn it off so it just draws at 100% opacity!