It's a pretty easy to explain this bug. If you sheer a white sheep, you're supposed to get white wool. If you sheer a black sheep, you should get black wool, and so on and so forth. I've tested it on every single possible color of sheep and here were the results when sheered:

White sheep: black wool
Black sheep: white wool
Yellow sheep: blue wool
Pink sheep: cyan wool
Lime green sheep: purple wool
Gray sheep: light gray wool
Light blue sheep: brown wool
Magenta sheep: green wool
Purple sheep: lime green wool
Orange sheep: red wool
Blue sheep: yellow wool
Cyan sheep: pink wool
Light gray sheep: gray wool
Red sheep: orange wool
Green sheep: magenta wool