Heimdall is the guardian of the Bifrost. In the movie Thor Heimdall is portrayed by Idris Elba, who happens to have dark skin. In the newer Thor series, Heimdall is drawn with black skin in the comics. But I know that originally he had pale skin, like Thor himself.
I want to know when this change happened and if there was an in-universe explanation.
I want to emphasize that I do not care about Marvel's motivation of the change and not necessarily if this is a simple retcon or not. I want to know when exactly it happened.