I just noticed people in the present are also using sober tones and I'm starting to think that the colorful tones may represent fantasy, as opposed to sober tones to represent crude reality. There will be more survivors and maybe each one will tell a different story and we shouldn't actually trust anyone's version as absolute truth.

[SPOILER from episode 8, select the text ahead] Ho Hang came back and he was still wearing a bright red jacket, but then he gave false testimony. Just a food for thought.

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"

I also think it has a deeper meaning... Especially since the reporters were all wearing it a few episodes later again...  BUT WHY

I just finished the drama and I still have no idea WTF the colors were supposed to mean. My best guess is that they represent the mood of the person wearing it, e.g. bright red for tense, green for satisfied and happy, etc.