When something like a black cloud passed between her and them, she knew that it was either a whale swimming over her head, or a ship full of human beings, who never imagined that a pretty little mermaid was standing beneath them, holding out her white hands towards the keel of their ship.

He fixed his coal-black eyes upon her so earnestly that she cast down her own, and then became aware that her fish’s tail was gone, and that she had as pretty a pair of white legs and tiny feet as any little maiden could have; but she had no clothes, so she wrapped herself in her long, thick hair.

Then the little mermaid raised her lovely white arms, stood on the tips of her toes, and glided over the floor, and danced as no one yet had been able to dance.

Then her sisters came up on the waves, and gazed at her mournfully, wringing their white hands.

The little mermaid leaned her white arms on the edge of the vessel, and looked towards the east for the first blush of morning, for that first ray of dawn that would bring her death. She saw her sisters rising out of the flood: they were as pale as herself; but their long beautiful hair waved no more in the wind, and had been cut off.

Andersen wrote that the little mermaid had blue eyes and she and her sisters had white skin.

You can read the original fairy tale here:

The Little Mermaid (Danish)You can read the original fairy tale here, The Little Mermaid Danish