It's even easier, actually. Get out the Smart Brush, the one with the gears on it, pick a black and white conversion style from the tool options, turn on the Inverse checkbox, and drag over the object you want to keep in color. The rest of your photo turns black and white, leaving only the selected object in the original colors.
You can also do it manually.
You need to duplicate your color photo.
1. Open your color photo in PSE10 Full Edit (A raw photo will open in camera raw to click the open image button too send it to the PSE interface)
2. On the Top menu click Layer >>Duplicate Layer >>OK
3. On the top menu click Enhance >>Convert to Black & White >>OK
4. If you can’t see the layers pallet to the right click Window >>Layers
5. At the bottom of the layers pallet click add layer mask (the icon with a small circle)
6. Make sure your foreground color is set to black then select the brush tool
7. Click the mouse over the area where you wish to reveal color and use like an eraser to reveal the background below
8. To correct errors switch the foreground color to white, then switch back to black and continue
9. Save as PSD to preserve your layers and if you wish make a jpeg copy from the PSD file using File >> Save As
N.B. if your brush is too big or too small you can use the square bracket keys to adjust the size up or down.
The smart brush tool has black & white options as mentioned by Barbara but it does involve making selections which can be more tricky than using the ordinary brush.