I think this has come up before, but I can't find it. Either way, I heard once that elves breed true. In "Evermeet: Isle of Elves", for example, a moon elf noble High Mage marries a gold elf uber-noble. They both keep their individual House names, and whenever a child is born silver, the child is accepted into the moon elf house, and vice versa. Basically, you do not get any watered down "silvergold"
variations: you either get silver, or gold.
The same goes for drow, and any other elven subrace. You could never get a halfdrow/halfelf elf, they would either be blackskinned, or silver/gold/copper-skinned.
I hope that helps.

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Cacie asks Larethiel 'Did that air just bow to you?