A combination of the gradient techniques described above were used to
create the Mac app icon below.
Gradient Maps
Quite different to other types of gradients, gradient maps can be a great
way to add color treatment, allowing for very precise control. Gradient
maps use the brightness of each pixel to map to a corresponding color in a
gradient.
If the gradient starts at red and ends at blue, then everything white in the
image will turn red, and everything black will turn blue. Everything in the
middle tonally will map to the gradient, depending on how bright it is.
The image below was used in a poster for Kingswim, a swimming school: