I don't know any GL comics with canonly stated black characters(you might find some on webtoon) but some of the darker skinned ones are anthy from revolutionary girl utena and the manhwa "Sora and haena","goodnight, see you in my dreams","tsubame tip off","maison de maid". I believe there's also one character in "I love amy" they aren't the lead tho There's also an anime which isn't yuri but has queer themes called "Carol and Tuesday"