I know this is a "bit" late...well, over a year anyway. The way I have done this is to open a colour image (then open a second one and change it to B&W) give one of the layers a different name - probably the altered one. Layer the B&W over the top of the colour then erase the area of this layer that you want the original colour to show through. In this case the eyes. Works well and is uncomplicated, it can also be done in many programs too.