system
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human
[asoiaf] Were purple eyes and silvery/gold hair a unique trait of the Targaryen family?

Or was it common among Valyrians? Or just nobles?
gpt
It was super common among all Valyrians.  The Velaryon family and Celtigar family also have it.  The Targaryens weren't a particularly special family in Valyrian, comparatively.  They were one of the weakest of the 40 dragon lord families.

But, about 400 years prior to the series begins, Daenys the Dreamer had a dream.  This dream led her father, Aenar, to leave Valyria and take up residence on Dragonstone.  Most of the other families were convinced that he'd only left because he was afraid of competition from the other families.  Aenar only took 5 dragons with him, out of which only one was alive by the time of Aegon the Conqueror.

Prior to the Conquest, it was not at all unique to the Targs.  Even in the current books, it's still not common to Targs.  Velaryons have it, Celtigars have it, Gerold Dayne has it, and at least one Hightower probably has it.