I know that I’m a white-female so my opinion is not as valid (edit: my opinion is slightly different being that I am not a person of color) — but what if, literarily speaking, this fictional future itself has less of a presence of the story of People of Color? What I mean to say is that, couldn’t it be purposeful that the show writers/producers left out that story to show how even-more-invisible the person of color is in this future where the ruling class is actually white and wealthy? Yes, they’re present and they’re still experiencing slavery but I think leaving out their story could actually be a comment on the fact that in this fictional future they’re just women, Handmaids. Their erasure could have continued on to be complete.
I’m not saying we excuse the writers for not including the story from a specifically POC perspective because, I think, it could add so much to this story. It would be another layer of political commentary, but it could be political commentary without their story as well.