Now, you have to lose the colors from the picture. Do this using Desaturate (Image/Adjustments/Desaturate or Shift-Control-U).

Next, duplicate the layer. For that, right-click and choose Duplicate or in the menu use Layer/Duplicate Layer. After that, invert the colors with Control-I or Image/Adjustments/Invert in the menu. You should see an image similar with this:

Kinda creepy, isn’t it? Lucky for you, you won’t have to show this image to your partner, cause I am sure it would spook him/her out of his/her mind.