In the good old days b&w images were captured by using b&w film.  Once photography moved to digital capture, b&w became just another option for photographers to exploit.  Similarly, sepia processing, which was done in the darkroom and not inherent in the film, also became available to us.  So in essence any image in this portfolio can be realized in either tonality.  However, some images simply don't want to work in one or the other of these two techniques, and often one can't tell whether a b&w image will go to sepia gracefully or not until one tries.

I find that I can "see" in either mode - color or b&w.  But my brain takes a few minutes to switch from one to the other.  Color creates compositional considerations which the human brain is uniquely designed to use, while eliminating it means contrast and brightness become the primary tools.