Hi!
I don't have a red lens unfortunately, otherwise I would compare the colour in my dad's Audi. I think red should be ok; I was thinking that if you added illumination you could keep the buttons white, and the display red so it would sort of match the looks.

Another question: how is the situation about the original A3 stereo? I mean, isn't that really heavily integrated? I hope not, of course, but I only saw cars with nav system, so maybe there are differences?