Narishma looks nothing like an Aiel... He's got dark eyes and hair, pretty much the coloring of Alanna Mosvani. He's described as having pale skin like her, by the way. He's sun darkened because he worked outdoor. Had he been a noble or merchant, he would have the dark but nordic look of Alanna (Arafellins seem to look a bit Finnish, their coloring anyway).

Sun-darkened skin is not a genetic trait of the Aiel. They have the appearance of the ancient celts, with pale eyes (blue, grey, green) and most of them have tones of blond or red hair. They've become sun-darkened because they live in the desert.

The Tinkers have largely lost the Aiel look over the millenia because they let any who adopt the Way join them. They're mixed blood by now.