That is because that level is part of a level pack where the HUD happens to be modified.Okay, unless something's wrong with my sight, I see the usually white-colored HUD text purple, but that's probably intentional.
That's intentional. Use fog, not colormaps.
Edit: Actually, if it was working like how I thought, the walls out of the water wouldn't be green either... Hmm..
So, I think this might be somewhat relevant to this report.
For example, stand under the red alarm in THZ2. Only the area you are in is red, not everything you see.
There might be some confusion because the colored ERZ gravity switches actually use fog, not colormaps, to produce their effect.
The official levels should probably switch to using fog, IMO, although I think the colormap is a faster effect.