Conan the Barbarian #64, "The Secret of Skull River!" Story by Roy Thomas, from a plot by John Jakes, art by Jim Starlin and Al Milgrom. (I'm not sure Starlin did much more Conan, but why not?)
The cover of this issue features Belit, but the story doesn't: running behind, a reprint of the Conan story from 1974's Savage Tales #4 was colored and slotted in instead. I had first read it in 1988's reprint book Conan Saga #10, and most comic shops should be able to get you the Dark Horse Savage Sword reprints--but both of those are black-and-white as well, Conan #64 is the only place to read it in color.