The same observation applies here. Khan has MAGIC BLOOD and we're nitpicking skin color?
Honestly? The (and I'm not going to call it "magic" blood because it makes us seem like apes banging away at the monolith) healing blood didn't bother me that much.
With respect, Star Trek has alway incorporated futuristic devices and solutions, introduced primarily to move the plot along (warp speed, transporter etc.). They don't spend a lot of time explaining them in any real detail, and most fans didn't belabour the issue. It was science fiction. We moved on (or we produced technical manuals.
Those who didn't accept this stuff at face value went out into the world to examine whether these things could really be possible. Anecdotally, many of them became scientists or doctors or aerospace engineers. That's the beauty of Trek. It introduces something because it is cool and convenient and that places a flag in the ground for others to reach for.
We already use blood and blood products to improve health and performance. We already know that hematopoietic stem cells (HSCs) from adult hosts can be released into the circulatory system to regenerate organs. We understand that cell death is suspended until long after the blood has stopped pumping. We have many examples of people who have died in cold conditions yet been revived. Canon established that Khan's genetic engineering gave him regenerative and healing abilities well beyond even that of normal men. How far fetched is it, really, that 300 years in the future we could know much more about harvesting HSCs and injecting them into a deceased, irradiated host that had been cooled after death, to effect cell repair?
Is any of this explained in the movie? Well, no. It does land as a bit of a WTF moment. But the more you think about it, the more you realise that it's just another in a long line of fantastic conveniences that Star Trek imagines and later generations make a reality.