I do it all the time! There are various ways to do it but here's my technique:
1. Change your photo into a grayscale image (Image>Mode>Grayscale)
2. Save it as something other than your original file name
3. Open your original (colour) photo
4. Drag the grayscale image on top of the colour one
5. Use the eraser tool to erase parts of the grayscale image, revealing the coloured photo underneath