Insert your photo into the word document from the insert tab or drag and drop.

Double click on the photo so it is activated and you see the picture tool tab at the top (pink).  Copy your photo (Ctrl c) and Past (Ctrl v) so there are two photos.

Double click on one of the photos so the picture tool is activated (it is the pink tab sticking up at the top) and go to the color drop down choosing the black and white option.

Double click the other photo so the picture tool is activated.  Click the remove background icon.

 Use the mark areas to remove until only the item you want color in is left.  You can add back if you delete too much.

When you have what you want in color, click keep changes (green check mark).

Click on the black and white photo and position it to the top left corner.  Do the same thing to the second photo with the color.

They will now be on top of each other so you can click on the black and white photo and send to back.

Finito.  Pretty cool you can do this in Word (only 2010).