Space gray but only because I like darker colors. Mine is Black sahpire, and it is true as most pointed out it hides 335IS details.
If you go with SG, get two tone light interior. Black interior will get old soon! Mine is Oyster/Balck, and it really brightens up the interior.
With AW Brown/Black interior looks incredible..
2014 F25 X3 M-Sport Carbon Black, Technology/Premium/Winter/Driver Assistance
2011 e92 335is DCT - Cobb, ETS IC, AFE DCI, BMW PS kit, M3 control arms, various cosmetic improvements RETIRED!
2007 X3 RETIRED!
2006 e90 330i 132k miles RETIRED!