There should be other potential solutions to this issue than the proposed one of simply inverting the sprite. While you've got the correct colour scheme going there, it's going to stand out from the rest of ADOM's new, beautifully rendered graphics like a sore thumb due to the glowing white outlines and there would probably be layering issues with the shadows and so forth that viewing changes to the sprite alone can't easily replicate.
More pointedly, the art has already been recoloured once. As an artist myself I appreciate how much hassle that can be, but it also means that direct recolours -are- possible, and so remedying this would be a matter of a few work hours at most; inversion isn't necessary if the art team are willing to refine it once again instead.
I'd like to take this opportunity to say that I greatly appreciate the changes which have already been made to the Dark Elf sprite so far, and that it's significantly better-looking now as well as more accurate to in-game lore. It would benefit from some further alteration in my opinion but what has been done already is brilliant progress.
[ADOM is simply much larger now with a far more connected player base. Even people who've been playing for over a decade (like myself, and like you) are going to find it harder to get our voices heard as the crowd grows larger and larger, but venting that frustration on the same thread that you're trying to draw attention to for positive change is going to have the negative result that your issue will seem less serious in response - which is a shame because frankly, this WOULD be a very welcome change.] It sounds like some of your ideas have been absolutely incredible, but still - don't assume that Thomas isn't listening. In my experience so far he's doing an absolutely sterling job especially given the number of bugs and RFEs reported daily! [Edits above render this section obsolete.]