It seems that the Designer colors do not match those available for coding.
I've just set the color of a button by Designer (ColorDrawable DarkGray) and then by code (created a ColorDrawable with Colors.DarkGray) and they do not match.
But wouldn't it be more helpful to stay consistent and only use color sets based on java/android design and not .NET because .NET has nothing to do with Android (it may be what the designer app itself was written in, but that should be transparent to the developer)?