What is the meaning of "washing sheep" in the calendar of Han Dynasty?

12 Zodiac forms six pairs of conflicting relations, referred to as six reds.

Six reds are: rat and horse, cow and sheep, tiger and monkey, hair and chicken, dragon and dog, snake and pig; When the relationship between six reds appears, it is called committing six reds, and everything will go wrong. The parties should try to avoid it.

In the calendar, not all sheep are washed, but which one is the same as that of the day. There are B sheep, D sheep, self-sheep, new sheep and expensive sheep. For example, if the ugly day rushes to the sheep, if the sky is dry, it means that the ugly day rushes to the sheep because there is wood.