Oddly enough this is not the first time that this has come up. 30 years ago when TWoK was released, many fans noted that most of Khan's followers were blonde haired blue eyed types including Joachim. In Space Seed, Khan's people were a more representative mix including Joachim. It was theorized by some that this particular group of 'supermen' had a sort of 'chameleon' adaptation in their genetics. This would certainly explain things quite well.
Ever notice that many of the same people who want variety in life frown very hard on vanilla... But without Vanilla, Baskin Robbins just wouldn't BE 31 flavors.