Si Collection, Lower Volume
Radical: Cow (niú)
Character: You
Kangxi Strokes: 9
Page 699, Entry 27
Broad Rhymes (Guangyun) and Collected Rhymes (Jiyun): Pronounced you (falling tone), same pronunciation as you (falling tone).
Jade Chapters (Yupian): Refers to a cow with black eyes.
Broad Rhymes (Guangyun): Refers to a cow with black eye sockets.
Also, according to Broad Rhymes (Guangyun): Pronounced xiu (falling tone); according to Collected Rhymes (Jiyun): Pronounced xiu (falling tone), same pronunciation as xiu (falling tone).
Literary Expositor (Erya), Chapter on Domesticated Animals: A cow with black eye sockets is called you.
Annotation: Refers to the eye sockets being black.
Explanation of Terms (Shiwen): You, pronounced same as xiu (falling tone).
Also, according to Collected Rhymes (Jiyun): Pronounced jiu (falling tone), same pronunciation as jiu (falling tone). Derived from Forest of Characters (Zilin). Meaning is the same.