What if you have found a nice image that you want to use on your site but it does not match your colour palette? Or, what do you do if you have decided to change the colour palette of your site but you do not want to change your graphics? This article explains some simple things you can do in GIMP to solve your problem.
As an example I will change the color of the image to the right. Now, if the colour was flat and not shaded then we could do a simple colour exchange. But because of the gradient, we need to be a little bit fancier in our technique.
Firstly, make sure that the image is in RGB mode and not indexed:
Image -> Mode -> RGB
Now select the colour that you want to map to by setting the foreground colour. Then do the gradient mapping:
Filters -> Colors -> Map -> Gradient Map
The image gradient should be around the base colour that you have chosen. In this example I am changing to #c6e675 (a pale green) as can be seen here.
The resulting image is too light for my liking so I will adjust the colour level to something darker:
Layer -> Colors -> Levels
The Adjust Color Levels dialogue box will allow me to adjust the Input Levels and the Output Levels. To get the affect I want, I slide the Input Levels to the right.
The resulting image is now something that reflects what I was looking for:
