The clarion call of Disney's Aladdin is to "not be fooled by commonplace appearances...for it is not what is on the outside but what is inside that counts." It would be wise for all those reacting to the casting of Halle Bailey as the new mermaid in Disney's remake -- be they mourners or grateful -- to heed that advice. And here's a Daoist consideration that, I am sure will sufficiently bother everyone: There is no white without the black, nor black without the white. The two concepts which we have labeled and projected since time immemorial depend upon each other and are frames for each other. When you realize the implications of this, you will come to know the Divine.
Yup, the beauty of the dialectic....
What's inside Halle is a sweet disposition and and otherworldly voice. Disney princesses are also outwardly beautiful and she is beautiful. That makes this a perfect casting.
Assuming this is art, artistic expression includes a license to be as derivative or as divergent from the source material as the artist wants to be. Therefore can be no right or wrong answer as to what the latest version of Ariel can look like because the colour of the previous Ariel is more or less irrelevant.