Open your photo in Photoshop.

Select Image > Adjustments > Desaturate.  This will turn the photo black and white.

Select the History brush tool from the menu on the left.

Brush over the area you want to bring the color back.  Make sure the Opacity is at 100%.  Use the Navigator (shown to the right) to zoom in for more detail.  Change the size of the brush from the drop down arrow located at the top left.

That’s it – easy peasy as Grace says.