i adore B&W but i feel color is what buyers want.
then lately i see some monochromatic shots on the frontpage.
but if you observe it's shots that does nothing for color...
eg. i shot a lovely black and white cat in an outstanding pose. i was about to submit it in color until i saw at one of the sites a black and white of a black cat.
so i thought again, and submitted it in black and white.
why would anyone want a color shot of a black cat , or a black and white cat? LOL
so, really, it all depends. if your images are better in grey scales,
i would send it in B&W.