How do you do colour isolation?

One of my classmates, for instance, took a picture of his girlfriend in her prom dress, and the whole picture was black and white except for her dress and the pink tones of her skin and lips.





So, how does this work? Is it something to do with the camera, or add-ons/accessories, or is it a photo editing (on the computer)?How do you do colour isolation?
It's not done with the camera...it's all post-capture work in Photoshop. You use the destaurate function, but you 'mask' out the portions you don't want to be affected by the desaturate. Masks are created by manual drawing or by more sophisticated tools like the selectors or magic wand.


An easier way is to have the color value radiate out from a specified central point. The farther you are from a central point, the more black and white the photo becomes. Not as accurate, but achieves a similar effect...kinda like a blur filter. It's a lot faster to accomplish than trying to trace a mask.





If you are working with a traditional b%26amp;w photograph made in the darkroom, the image is colored in manually by special paints or markers.How do you do colour isolation?
when I have done this in the past I have used photoshop with a combination of the magic wand and polygonal selection tool wo highlight the area that you want in black and white.... and do it that way.





If anyone has an easier way to do this with high quality results- I'd love to hear it.