What is the title of a science fiction novel with futuristic society where people lived hundreds years and were called because their skin had gone translucent?

Here are a few title ideas, playing with the concept of translucent skin and long lifespans:

Playing with "Translucent":

* The Shimmers

* Underneath the Skin

* The Glass Age

* Pale Sun

* The See-Through Century

Focusing on Longevity:

* The Hundred-Year Cycle

* Eternity's Echo

* The Ageless

* Living Memories

* The Long Tomorrow

Combining Both:

* The Transparent Century

* Shimmering Lives

* The Ageless Shimmers

* Beyond the Flesh

* The Skin of Time

Other Ideas:

* The Twilight People

* The Whispering City

* Echoes of the Past

* The Immortal Canvas

Ultimately, the best title will depend on the specific tone and themes of your novel.