Here is a link to a site that does what I did with the apple and berry picture. It is a different process and looks to be easier to do. It is using photoshop but I will see if I can do it in Gimp.
I just did a search to find tutorials using GIMP and there are many. Here is one that manages to keep red apples and has a black and white background, just like what I did using Photoshop. http://graphicssoft.about.com/od/gimp/ss/partialcolor.htm
Have a look at it and give it a try.
On Tuesday we will go through the process of photo editing a picture using Gimp.
We will also continue with our discussion of "Exposure Triangle" and how to go beyond "Automatic" on our digital camera. Bring your camera and manual.