-The African-American father and son: Michael Dawson and Walt Lloyd
Even in a TV Guide interview, Harold Perineau (who plays Michael) had some critical comments to make about how this storyline got "resolved":
TV Guide: Were you disappointed Michael and Walt didn't reconnect before your character died?
Perrineau: Listen, if I'm being really candid, there are all these questions about how they respond to black people on the show. Sayid gets to meet Nadia again, and Desmond and Penny hook up again, but a little black boy and his father hooking up, that wasn't interesting? Instead, Walt just winds up being another fatherless child. It plays into a really big, weird stereotype and, being a black person myself, that wasn't so interesting.
-Speaking of Sayid and Nadia, it seemed unbelievable that in the "sideways" afterlife timeline, Sayid's "soulmate" was the blond Shannon instead of his childhood sweetheart. We saw his love and devotion to Nadia drive him to incredible lengths both before and after the crash (shooting himself so that Nadia could escape prison, working for the CIA, working as a hit man for Ben, etc.) but he's going to spend the next level of eternity with Shannon?
-The African drug-dealer Mr. Eko's stay on the show was relatively short-lived and he didn't even come back for a cameo in the last season, but that seems to have more to do with behind-the-scenes constraints of the actor Adewale Akinnuoye-Agbaje rather than the writers and producers of the show.
-Also a bit disappointing was the 6th-season episode "The Candidate" where the last few major brown and yellow characters (Sun, Jin and Sayid) were killed off all at one go.
-Given all the emphasis on Aaron, what happens to Sun and Jin's baby?
-What's the story behind the big statue of Taweret and the hieroglyphics everywhere? In my mind I imagine that some ancient African alchemist/numerologist/scientist/mystic was trying to find the elixir of life or a perpetual motion machine and inadvertently discovered/invented the Light at the heart of the island. A side-effect was that the land surrounding his laboratory/temple, including the statue, was transported out to the Pacific to the island. Of course, I'm not a writer for Lost so for all I know Allison Janney's crazy mother character built the statue single-handed.
-I'm still thinking about how to process Hugo "Hurley" Reyes and Richard Alpert/Ricardo/Ricardus in terms of the racial dynamic of Lost but basically they are white (and Hispanic).
Lost (&Heroes) Hate Black People
Bitch Media: The Numbers–Lost and Race and Death on the Island looks at the body count on Lost through a racial lens.
Hollywood Insider: Harold Perrineau on his departure from Lost: "I was disappointed... I wouldn't say I'm bitter" which follows up on Perrineau's comments to flesh them out and give them more nuance (i.e. walk them back).