Working with Black-and-White and Color Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 336

4.4.4 Using the Colorify Filter to Color an Image
Filters provide yet another method to colorize images. You can find the
Colorify filter in the Colors menu.
If you select this filter, a dialog appears that allows you to select a color
from a prepared color palette. Alternatively, you may click the Custom Color
button to select a color. Clicking this button will display the familiar Color
Picker, where you can select any color. Using the Color Picker or the Colorify
dialog, click OK to accept the color you selected.
The image will be uniformly colored with the chosen color. However,
you may notice that the colorization looks rather like a color overlay, much
more so than it would if you used the Colors > Colorize method. Be aware that
additional options, such as saturation and brightness, are not available for this
function.
There is only one way to modify the brightness, and that is by using the
Colors > Brightness-Contrast or Colors > Levels menu item. Similarly, you can
correct the lightness and saturation by using the Colors > Hue-Saturation
menu item.
Figure 4.31
The Colors > Colorify dialog and its Color Picker