Queen Zixi of IX by L. Frank Baum — Read

Now, as might be expected, Queen Zixi lost no time in endeavoring to secure the magic cloak. The people of Ix were not on friendly terms with the people of Noland; so she could not visit Princess Fluff openly; and she knew it was useless to try to borrow so priceless a treasure as a cloak which had been the gift of the fairies. But one way remained to her -- to steal the precious robe.

So she began her preparations by telling her people she would be absent from Ix for a month, and then she retired to her own room and mixed, by the rules of witchcraft, a black mess in a silver kettle, and boiled it until it was as thick as molasses. Of this inky mixture she swallowed two teaspoonfuls every hour for six hours, muttering an incantation each time. At the end of the six hours her golden hair had become brown and her black eyes had become blue; and this was quite sufficient to disguise the pretty queen so that no one would recognize her. Then she took off her richly embroidered queenly robes, and hung them up in a closet, putting on a simple gingham dress, a white apron, and a plain hat such as common people of her country wore.