You might like to try using a mono layer of your pic, overlayed onto a colour layer of the same pic, then click on the layer mask button on the bottom of your layers pallette, which gives you a layer mask (white box next to the thumbnail of your pic in the layers pallette). Click in the white box, choose a soft edge brush of suitable size, then make sure your colours are the black and white default, then paint over the area you wish to make colour. This then adds or subtracts the mono layer, leaving the colour to show through. Being a mask, you can undo any mistakes.