Photoshop :: Convert A Color Photo Into Black And White

I want to covert a color photo into black and white but bring back a certain color. How many ways are there to do this? Which method is the most professional (as in provides the most professional finished product) I've read about doing it using the paint brush to bring back the color, also the color selection tool.

The particular image I'm trying to achieve this on is not so simple. The part I want to bring color back into is a dripping pink ice cream, so there are small drips and blobs, often with fair skin color in the background. Ice cream is dripping down face and hands and body and I want to preserve these details accurately. The bits I need to bring back aren't large blocks of color so I'm finding it very difficult to achieve a professional look.