In this tutorial we will learn to colorize eye in green color.

 1. Open the image in GIMP software. create a new layer with transparent background.

 2. In layer box select this new layer as multiply.

 3. Select the new layer. Select the green color from color tray and then select the brush from tool window.

 4. Zoom the image and fill the color in the eyes.

 5. Finally it comes to be. Select Layer > Merge down. Now you can save the image to desired destination.