How to make fuzzy colored back ground of an image in GIMP.
1. Select the required image.
Just to explain, I have selected the below one.

imageselected

2. Select the free select hand tool from the tool bar and select the region required. Like this.

freeselecttool

3. Then select the 'Invert selection' from select in the image menu

selectinvert

4. After doing so, select the blend tool from the tool box

blendtool

5. Select the required gradient from the gradient choose

selectgradient

6. Drag the arrow on the image

dragthearrow

7. The view of the image would be like this.

finalimage


The image with fuzzy colored background is done.

You may also change the shape of the gradient for different shapes.