B&W Editing Assistance

[marigold35]

A have a question about digital editing: How do I keep select objects in colour when I convert an image to black and white? For example, in the images below, my client requested the photo in B&W but keep the purple in the photo, e.g. flowers, neck tie, etc...

If anyone has a link to a video that would be awesome. I work with Lighroom 6 and Photoshop CC. I have been a photographer for many years, but I am still learning more and more about post-processing. I think my job on the colour in this image is not great either... Any feedback is appreciated. Thank you!