What is the preferred color for a sacrificial sheep?

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The best color for a sacrificial sheep is white. Evidence for this is found in the narration that the blood of a white (afra') animal is purer to Allah than the blood of two black animals, narrated by Ahmad with similar meaning. Abu Hurairah stated that the blood of a white animal is more beloved to Allah than that of two black animals. Furthermore, whiteness was the color of the Prophet's sacrificial animal. Generally, the best color is preferred.