I've discarded my previous theory and went with the simple "it's just a way to mark the timeline before and after the accident" but they were using that hideous beige again in some present scenes in episode 9 and 10, so I don't know anything anymore... The recently found survivors were wearing coloured clothes, but more darker and sober tones, as opposed to the blatant full-saturation bright ones they've been using. From all the complaining about unrealisticness and the weird choice of flamboyant tones, I'll stick back to "it's a way to delimit reality, fantasy and the in-between mix"