B&W photo histogram shows colors

[PeterAit]

I have used LR to convert a photo to B&W yet the histogram still shows some colors. What is this all about?

[digitaldog]

To be expected depending on the camera profile selected and reflected upon the Histogram. Try selecting an Adobe B&W profile, different?

[mcbroomf]

The only way I can get colour separation in the histogram after a B&W conversion is if I use the Colour Grading panel to add some kind of tone (eg Sepia), then the colours pull apart.  When I just click on B&W the histogram has all colours overlayed. 

I don't see a Monochrome option in my profiles (only Adobe Monochrome) that you are showing so I wonder if it has a built in tone adjustment.

[digitaldog]

With raw data, the Histogram shows you that, in Melissa RGB, the current rendering instructions and a camera profile. There isn't anything wrong or unusual about what you show here. Once you render everything above into a color space, then you'll see the effective Histogram of all that. So if you were to render and encode into a gray gamma* color space as, say, a TIFF, now you'll see a different Histogram with 'no colors' in it. I'm not sure why anyone would even want a 'monochrome' single-channel grayscale document, but that is possible.
*You'd likely have to do this in Photoshop or similar, as I don't see that LR/ACR exports anything but RGB profiles.