This seems to be a fairly common issue! I wonder if the OP is leasing. If he is, perhaps BMWNA has some color combinations flagged as being "unusual" (for lack of a better term) and they want dealers to discourage these orders as it makes the resale after the lease is up more difficult. Just a guess...
2011 Space Grey E90 M3, DCT, Comp. Pkg.
1997 Z3 2.8, Artic Silver, Tanin Red interior, MT
1974 2002tii, Inka, MT