You won't find Tanzanite on an M3 -- all the more reason to get it yourself! The color hasn't existed long and pics of it on ANY car are tough because dealers can't order semi-Individual colors for floor models, only Priority 1 cars (built to a paying customer's spec), I believe. Just take a look at the 640d Gran Coupe and 650i Convertible at the Geneva Auto Show and use your imagination.
Tanzanite at Geneva: http://www.6post.com/forums/showthread.php?t=495046
Tanzanite in the sun: http://www.6post.com/forums/showthread.php?t=723828