The closing discussion in the perek revolves around a question of ḥatzitza – of a separation – that would keep a ritually defiled object from becoming purified when placed in a mikveh. This discussion does not relate specifically to the laws of the Temple, but to other situations when an object is to be purified. Does a spot of blood or grease on the object keep the purification from taking effect?
Rava states that it is obvious to him that if there is a spot of blood on clothing it will act as a separation and will preclude the possibility of ritual purification. An exception to this ruling is a case where the owner of the clothing is a slaughterer. Such a person always has such spots on his clothing and he is oblivious to them. Similarly, if there is grease from fat or wax on clothing, it will act as a separation, unless the owner deals in those substances. Since such a person will always have clothing that is spattered with fat or wax, he pays no attention to them, and they are considered unimportant. The general principle is that the laws of ḥatzitza are subjective, and a spot or stain will only be considered a ḥatzitza if the person cares about it and would ordinarily remove it.
Rabbeinu Tam understands that Rava’s teaching applies not only to clothing, but also to spots on a person’s body. Therefore he rules that if there is a relatively small spot on someone’s body and that person is not concerned with it at all, it would not be considered a ḥatzitza. The Rashba even has a reading of our Gemara that specifically has Rava talking about a case where the spot is on someone’s body. Based on this the Shulḥan Arukh rules that when a woman dyes her hair or paints her face, that would not be considered a ḥatzitza and her ritual immersion would not be affected (see Yoreh De’a 198:16-17).