I vote for white

 

Changing the gauge face on the instrument cluster is a pretty big deal - it involves removing the cluster, removing the acrylic cover, removing the needles...and finally an exact-o knife to cut rubber grommets that hold the face plate in.

 

I had black in my first 911, a 1990 C4 Cab. I miss that look, as my C2S has the white gauge faces. I think black is best for 2 huge reasons:
- more classic, as someone else alluded. (for me, I have the reminiscence as well)
- much cleaner look, due to the cut-outs for the digital items. As you see in the pic with the black gauges earlier in the thread, compared to the others, the faces themselves, (not the numbers) look more mono-tone with black vs two tone with other colors (gauge-face color plus the cut-out in dark-grey / black)

Of course, offsetting that is either the uniqueness, bling factor, or tie-in with other colors (belts, exterior color, etc). I have red belts, red calipers, etc, so red would be a decent choice. White makes no sense to me. +1 to the posted above: I wish I had black...
and I'll add - I miss it wasn't such an astronomical expense to change them