You're saying that a few decades spent in the ceti system could have turned Khan's skin as pale as it was in TWOK?
I don't recall the Khan of "Space Seed" being all that swarthy?
Perhaps his sleeper unit in the Botany Bay doubled as a tanning bed? Perhaps he was always pale, but had a tan before climbing in for the long sleep?
Harrison or Khan?
by Therin of Andor
, on Flickr