that is pretty wild. I actually googled and found the same site you did.
this stood out to me here: "The color-graded hues sit somewhere between black, white and gray, but why wasn’t the full color spectrum utilized? Probably to protect the audience from the nonstop blood and gore projected on screen throughout its 2-hour, 12-minute runtime," Deadline's Valerie Complex wrote in her review of the film.
also this: Variety noted that crimson hues are prominent in Emancipation's final battle scene, specifically present in the Confederate flag, the Union banner, and, naturally, in blood. This type of symbolism can be compared to the little girl in the red coat in the otherwise black-and-white 1993 film Schindler's List.