Depending on how light/dark you want them smoked, you can use Niteshades or Testor's Transparent black spray paint. Niteshades will give you a darker tint with the first coat, while Testor's goes on much lighter. Good Luck!

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2003 530i, Silver on Grey, BC Coilovers, Square 9.5" M-Parallels, Gloss Black Roof
2007 328i, Alpine White on Black, Sport/Nav/Premium
SOLD: 2006 X5 4.8is, Lemans Blue on Black