Recently I have started experimenting with exploiting the lovely shades of colors that emerge when a photo is taken that is quite out of focus. This was prompted one day recently when strolling along in Bong Park with my Sigma 150mm f2.8 macro lens photographing the wild flowers growing along a path. I had accidentally left my (manual) focus at the wrong setting, but was quite pleased with the resulting image!
 

On the left here is an out-of-focus shot of a group of Yellow Echinacea Coneflower flowers. One can enjoy the image by simply noting the shading of the colors from patches of yellow to surrounding hints of purple and a variety of shades of green. The overall effect is quite a pleasing soft-toned montage of colors.
 

Here is the same photo but this time focused on most of the flowers. This image is quite bland with poor composition and lacking interest. Though all the same color elements are present, the photo overall does not serve to bring out the colors.
 

   Here is a favorite of mine taken the same day (left). While one can just make out the shape of the purple Coneflower, the dominant feature of the image is the pleasing shades of purple, dark red, yellow, greens. These soft gradations of color provide a mood of calm and tranquility and the sheer beauty of the colors stand out to be enjoyed.
 

The same image, but this time taken properly focused (right), is certainly more technically correct of course, but the overall impression one is left with is a photo of yet another flower - no particular interest. In fact the out-of-focus coneflower on the bottom of the image is a bit distracting, whereas the same coneflower in the deliberately out-of-focus image on the left actually contributes to the variety of colors overall.
 

To take photos like these one has to work with manual focus of course. Many simpler cameras (point-and-shoot, cell phone, tablet) don't have this feature; single lens reflex cameras do. Furthermore an SLR camera allows for full control of all the parameters that go into a properly focused and exposed image. In addition these type of cameras also allow for lens interchangeability - hence a macro (close-up) lens that makes these sorts of photos possible.