first of all your original post doesn't seem very, yk, open to the interpretations of other people. like:
Let's please just admit that ALL TOLKIEN'S ELVES ARE WHITE.
I understand that people in fandoms often spit on the canon, spit on the opinion of the author and they don’t care that Tolkien saw his mythology as “northern” (Germanic-Celto-Finnish, one might say), and I ignore it when it comes to the Ainur , for example, but... but Tolkien's elves are all white!!! Why can't people portray at least canon characters canonically?
that's hardly an invite to reimagine things! you're complaining that you can't even find a single fanart of white, er, canonical Fingon unless you go in certain parts of the fandom and saying that people should admit that 'all tolkien's elves are white'. wow, such a bold new statement!!! never heard before!!!! especially not from 'anti woke' reactionaries!!!!
However, people should realize that this is NOT canon in the texts. Texts are primary material, we need to be guided by them, and the fact that the author has died does not mean that we should stop respecting him.
Tolkien isn't Jesus Christ, or any other religious figure considered above criticism. he was a human being that we can appreciate for some of his qualities, AND at the same time admit that he'd flaws. acting as if he can have no flaws is a dangerous mindset that puts him on a pedestal and makes us unable to treat him as it's due, aka as if he's just a person like all of us.
AND a big flaw of him was a personal view that puts Europe (or, as you said 'the general mood of Northern Europe, which includes not only the scandinavians, but also the anglo-saxons, the island celts, the finns and even the balts and some slavs') at the center of his personal idealized world whereas 'tropical Africa', and any other land that was 'foreign' to Europe at the margin. thus when he was born in South Africa of all the places, it's not that like he never set foot outside of Europe in his whole life.
does this mean that he should be discarded or that his work was unworthy of any consideration? no, but you can't have the absolute audacity to come at the Tolkien fans who INSTEAD want to 'fix' this fact with fanarts and fanfics by telling them that no, they've to admit that there's no space for any not-European reality in Middle earth!!! because that would be a very real insult to Tolkien !!! oh c'mon.
Why not take on Tolkien's existing Harad? Why repaint white regions if it already has regions populated by people of color? That's funny.
there ARE fics and fanarts about 'Tolkien's existing Harad', but guess why? most of them end up being original characters and/or stories that are almost original settings (and therefore, much harder to get attention than the characters and stories we know from the text) because jrrt per sé never bothered too much with those regions, so the fans have to completely made up a new setting with like, 2 informations in toto. yeah you can do it but at this point it's almost like writing an original story. this is ALWAYS for jrrt's mindset i've said before, the whole ' i only see Northern European cultures as worthy of my attention' part.
so, after we've admitted that everyone in the Tolkien's world is Northern European and that therefore anyone foreign to those latitudes shouldn't be included, what are we going to do then? which kind of contribution are you trying to bring with this fact? that people should stop of drawing any elf in a way that's not 'canonical'? sorry but that speaks for itself. ugh!