I used the blue lights for two reasons. 1) Yes the down light that came with the car is blue to start with. So I wanted to match that and that's what the factory kit is as well. 2) I had Red down lights in my former A6 and wanted to do something different from that car. Yes the red is cool too and it doen't effect your night vision, but I think that the output of these lights is so small and none of them are directed at your eyes squarely, so your night vision should remain the same.
And blue is Techie Cool!
Also, I dug into the blue down light installed in the dome light area and removed the factory Neutral Density filter that sits right in front of the Blue LED. The light now actually lets you see things in that area. Before it was just a dim, faint blue glow.