Working with Black-and-White and Color Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 344

Now we dedicate our attention to the details:
• Duplicate the portrait-colored layer.
• Rename the layer portrait-mouth .
• Position it above the portrait-face layer in the Layers dialog.
• Use the Free Select tool (Lasso) tool to select the mouth.
• Choose Select > Feather and set it to 8 pixels. Then invert the selection
with the Select > Invert menu item.
• Delete everything except the mouth using Edit > Clear .
• Then choose Select > None to close the selection.
• Again, select the Colors > Levels menu and use the red channel, modifying
the mid-tones, to color the mouth.
• Choose the Colors > Brightness-Contrast menu item to correct the contrast
and brightness of the mouth.
• What remains is to give the eyes a natural appearance. Return to the
portrait-face layer.
Now use the Free Select tool to select the whites of the eyes and the pupils.
• Choose Select > Feather and set it to 5 pixels.
• Choose Colors > Desaturate .
• Choose Select > None .
• Use the Ellipse tool to select the pupil area.
• Then use the Free Select tool to remove accidentally selected areas from
your selection.
• Choose Select > Feather and set it to 5 pixels.
• Choose Colors > Colorize to select a color for the pupils.
• Choose Select > None .
• Save your image.