If you are looking for the truly "timeless" shell color, I say go with Pearl. The outside doesn't matter, as it goes with everything.
Outside pearl, Sterling marble hides the water spots pretty darn well, and is as close to timeless as pearl is.
Champagne Opal looks elegant, but It will show water spots during the day for sure, same thing with Tuscan, but people still like both those to let a little water spots stop them from choosing those colors.