In this tutorial, we will teach you how to change color in Gimp. For this tutorial, we will be working on a free stock image. You can download the image from the following link:
http://www.freeimages.com/photo/600725
In the image, we will be changing the color of the wooden front portion of the bird house only, leaving the rooftop, the background and the base as it is. So download the image, bring it up in Gimp and let's get started.

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Step 1 - Making a path of the object
First of all, we will select the path tool from the toolbox on the left. With that done, let's move to the canvas and start making a selection of the wooden front area. So let's head up to the top of the birdhouse, and start making anchor points over the image to make a selection path.
Do remember to carefully make the entire selection path. For example, see the highlighted area in the image below and you will notice a small gap between the rooftop and the actual body and the blue sky is also showing in the background. You would have to stick to the edges of the body so that the background is not included in the selection path.
Some of the background might accidentally get included, so simply press CTRL Z to undo the last addition in the selection path and you can add that anchor point again, this time making sure that none of the background gets included. The same has to be done for the base and the rest of the body.

Step 2 -- Making a selection from the path
Once you have made the path, right click within the boundaries, move over to "Select" and click on the "From Path" option. This will turn the path into a selection

Step 3 -- Creating a new layer
With that done, let's create a new layer by clicking on the "New layer" button highlighted in the image below. After that, the new layer window will open up. Over here, make sure that the transparency option is selected for the layer fill type option. Once you click on the OK button, the new layer will be created.

Step 4 -- Painting over the selection
Now the idea is to use a different color within the selection on the new layer. So pick up the brush tool in Gimp, change color and select a shade of green. You can select any color according to the image you are working on. After that, simply increase the size of the brush and start applying it all over the selection.
Remember to cover the entire selected area. If you miss out any spots, that would be clearly visible and the effect won't look realistic. With that done, deselect the selection by right clicking on the area, moving over to "Select" and clicking on the "None" option.

Step 5 -- Changing the blend mode
Now we will move to the layer panel and open up the layer mode drop down menu. Make sure that the colored layer is selected before opening up the menu. Over here, select the overlay option so that the new color blends with the original background image.
And there you can see that the color of the body has changed.

Step 6 -- Adding the final touches
Now let's add a few final touches. For example you can see that it looks like someone painted yellow over the wooden perch in the image (see screenshot below). So let's carefully apply the eraser tool over here so that it looks more realistic. You can decrease the size of the brush and make sure that you carefully follow the edges so that it isn't applied on the body of the birdhouse.
Similarly you can apply the eraser over the entrance hole as well.