With this project (selective color project), we had to take portraits and then use photoshop to make the whole image black and white except for one part. For the most part I would pick the part of the image that is the subject or has the most vibrant colors (For example the book is the subject or the red hull of the boat in the background). I believe that doing this makes the colors "pop" more. When all the colors in an image are present, you get this sort of "color-blindness" to some of the less relevant colors, and the main colors just start to mix together with the background colors. So when you single out one color or object, you notice the colors more.