Age tanning is mild to moderate and uniform.

The Pool of Fire - the third book in John Christopher's "Tripods" trilogy.
[the back cover copy of a later edition]: "Will Parker has managed to escape from the City of Gold and Lead, where he served as a slave to one of the Masters who rule the modern world. And he has not only discovered what lies behind the Tripod's power, but how the Masters heartlessly plan to destroy Earth. The free people - those who have not been Capped and enslaved - must quickly devise a plan to defeat the Masters. Yet even as they do, they do not think of the most important matter: Who will rule the world once it has been freed?"