I agree with William. Shoot in color (raw/jpeg) and you will have more options in the future. I've never been satisfied with any in-camera b/w or monochrome, and I might later decide to render the photo in color.
You can set the Picture Control to "monochrome". If you are shooting raw files, this is just a flag in the file that most non-Nikon software will ignore. For JPG files, the camera's conversion will be baked into the picture. As previously noted, software conversions to b&w will usually get you better results than the camera's conversion.
The big advantage to using the monochrome setting when shooting raw files is that the camera will show you the b&w version on the LCD so that you can see any potential exposure problems while the flag in the raw file is easily used or ignored as you want in post processing.
---------+---------+---------+---------+---------+ Joseph K Seattle, WA, USA
I sometimes capture images in color that I think would look good in monochrome. Then I employ more flexible post processing software to bring out the full quality from my perspective. Look at something like NIK's Silver EFX Pro as an example. I can vary the contrast, apply filters, add a film texture, grain and a lot of other great effects.
Joseph's comment about previewing in monochrome is about the only reason, other than convenience, I see for using the B&W feature of the camera.
You might try an experiment. Take an image using the in-camera B&W option. Put it away and try not to look at it. Then take the same exact image in color and post process in Lightroom, adjusting the image to your taste. Once you're done, compare the two images and see if you like what the camera has done. That will help you decide if you want to use that feature on a regular basis or not.
"Red is gray and yellow white, but we decide which is right ....and which is an illusion"