Actually those 2 series are spin-offs of 2 big-budget french films adapting Dumas's Three Musketeers that will be released in France next year. (see here https://www.imdb.com/title/tt12672536/?ref_=ttfc_fc_tt )

The "black musketeer" is a new character created for the films and played by french actor Ralph Amoussou. The name of the character is Hannibal and the writers said he is inspired by Aniaba, a prince of West Africa who gained the title of musketeer in France (but under the reign of Louis XIV, not Louis XIII like in the novel and film, so it's not a direct adaptation). I guess that Ralph Amoussou will reprise the character for the TV show.

Regarding "Milady : Origins", Eva Green is playing the character in the films but I'm not sure she'll reprise the character for the show, as the character would surely be younger.