The shimmer

"The day I realised my shimmer was entirely gone, I cried, and cursed the wretched foreign lands my lord had sent me to. When I found it in my skin again after my return, I held a feast on that day every year."
— Syfa han Dannas, ambassador

All inhabitants of Gdera have "the shimmer". It's a gleam of the skin and hair, like powdered metal, and considered rather attractive. Humans, however, shine and don't just shimmer, in an amount that can cause eye damage. Because of the humans' need for it, many cultures wear ornamented eye protection.
Travellers acquire the shimmer soon after their arrival in Gdera and loose it after their departure; again, not humans. The shimmer is an honour badge of sorts, and Gderans look down their shimmering noses on those who have none.

Artist's notes
The strong eye makeup of desert peoples from the Egyptians onward is in fact protective against sun and parasites. I always liked adding decorum to portraits, and have a wide range of choices from mud to silk veils with the shimmer. In any case, distorting faces with patterns or hiding them behind veils and masks is an interesting character design feature.