Labial color is darker, nigrescent reason?

嘴唇颜色比较暗，发黑的原因？

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In front of the door, there was no signboard of America Hotel hung, it was the same as other house, there was a heap of nigrescent firewood, and a washing line for drying clothes.

门口并没有挂什么“美国饭店”的招牌，和别人家一样，堆着一堆发黑的柴禾，拉着一根晾衣裳的绳子。

youdao

In front of the door, there was no signboard of America Hotel hung, it was the same as other house, there was a heap of nigrescent firewood, and a washing line for drying clothes.

门口并没有挂什么“美国饭店”的招牌，和别人家一样，堆着一堆发黑的柴禾，拉着一根晾衣裳的绳子。

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