Black and white is not the issue, form is.

Black and white provides the means to express the essential form of a brandmark. It provides the highest contrast between figure and ground and is the most simple, clear and demanding version.

Even if the brandmark doesn't get used in black and white in application it is the strongest position from which to work to ensure the brandmark is properly resolved.

Clients may never require the black and white version directly but they should always ask for it.