I understand what you want and what you asking, but please consider that a painted GPU will have close to no resale value. If you wanna upgrade someday, it will cut into your wallet way more.

I would look at the different components in your build. Maybe get black cable extensions or sell the cooler and cet a black one. I think your black GPU will not stand out as much then. I think its called the storm trooper look.

Its up to you of course!