How to get a black and white photo with most vibrant colors showing?

My sister has a compact digital camera made by canon. When she was taking pictures she was able to put it in black and white but have it automatically pick out the most vibrant color and show it in the black and white photo. She was able to do it automatically by just changing the settings on her camera. I would like to know what the name of this function or setting is and if Nikon makes any cameras that have this ability.

Use crayons

I'm not sure about the Nikons, but why would you want to do it in the camera when you can edit the photo through a photoshop program. It will be better because then you will have a black and white picture and the original in color. Also, if you want a more vibrant photo, through photoshop, you could raise the contrast and brightness. Professional camera usually don't have this setting built in for a reason btw! So, I highly suggest you get photoshop, you will be able to do more than your friend.