This has been confirmed upon in Avengers: Endgame, in short the Asgardians, presumably half of them, escaped to Earth and created "New Asgard". Of the half of the Asgardians that survived the named characters we see are:


From looking around a bit the change in the comics appears to have first been shown in Loki Vol 2 Issue 4 which was released 16/03/2011 which is before Thor came out in 27/04/2011. Of course though the casting for Heimdall was already known by then. As such the change to dark skin was probably done because of the casting of Idris for Heimdall. An in universe ...

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